Rozprawy doktorskie na temat „Carbon nano structures”

Carbon fibre reinforced plastics (CFRP) have revolutionised industries that demand high specific strength materials. With current advancements in nanotechnology there exists an opportunity to not only improve the mechanical performance of CFRP, but to also impart other functionalities, such as thermal and electrical conductivity, with the aim of reducing the reliance on metals, making CFRP attractive to many other industries. This thesis provides a comprehensive analysis of the nano-phase modification to CFRP by growing carbon nanotubes (CNTs) on carbon fibre (CF) and performing mechanical, electrical and thermal conductivity tests, with comparisons made against standard CFRP. Typical CFs are coated with a polymer sizing that plays a vital role in the mechanical performance of the composite, but as a consequence of CNT growth, it is removed. Therefore, in addition, an ‘intermediate’ composite was fabricated – based on CFs without a polymer sizing – which enabled a greater understanding of how the mechanical properties and processability of the material responds to the CNT modification. A water-cooled chemical vapour deposition system was employed for CNT growth and infused into a composite structure with an industrially relevant vacuum-assisted resin transfer moulding (VARTM) process. High quality CNTs were grown on the CF, resulting in properties not reported to date, such as strong intra-tow binding, leading to the possibility of a polymer sizing-free CFRP. A diverse set of spectroscopic, microscopic and thermal measurements were carried out to aid understanding for this CNT modification. Subsequent electrical conductivity tests performed in three directions showed 300%, 230% and 450% improvements in the ‘surface’, ‘through-thickness’ and ‘through-volume’ directions, for the CNT modified CFRP, respectively. In addition, thermal conductivity measurements performed in the through-thickness direction also gave improvements in excess of 98%, boding well for multifunctional applications of this hybrid material concept. A range of mechanical tests were performed to monitor the effect of the CNT modification, including: single fibre tensile tests, tow pull-out tests (from the polymer matrix), composite tensile tests, in-plane shear tests and interlaminar toughness tests. Single fibre tensile tests demonstrated a performance reduction of only 9.7% after subjecting the fibre to the low temperature CNT growth process, which is significantly smaller than previous reports. A reduction in tensile performance was observed in the composite tensile test however, with a reduction of 33% reduction in the ultimate tensile strength, but a 146% increase in the Young’s modulus suggests that the CNTs may have improved the interfacial interactions between the fibre and the polymer matrix. To support this, improvements of 20% in the in-plane shear stress and 74% and the shear chord modulus, were recorded. Negligible differences were observed using a pull-out test to directly measure the interfacial strength as a consequence of the inherently difficult mechanical test procedure. The fracture toughness was tested under mode-I loading of a double cantilever beam configuration and improvements of 83% for CNT modified composite alluded to CNT pull-out fracture mechanism and crack propagation amongst the microstructures. The changes in the physical properties are correlated to the microstructure modifications ensured by the low temperature CNT growth on the CF substrates used in the CFRP composites. This allows for a new generation of modified multifunctional CFRPs to be produced.

Fabrication of ordered anodic alumina nanopore arrays and anodization parameters including electrolyte, concentration, voltage, temperature and time have been investigated. Cobalt nanoparticles were electrodeposited at the bottom of the pores. Vertically aligned, open-tipped multi-walled carbon nanotube arrays of high density and uniformity were synthesized via a flame method on silicon substrates using a nanoporous template of anodized aluminum oxide. The diameter and length of the nanotubes are controlled by the geometry of the aluminum oxide template. It is the cobalt catalyst particles, not the porous aluminum templates, help the growth of carbon nanotubes through graphitization and bonding of carbon nanotubes to the silicon substrates. Fabrication of nano-structures has been demonstrated. Nano-trenches of 20 nm have been achieved using single-walled nanotube bundles as shadow masks, which were aligned across electrodes under high frequency AC voltage.

Thesis (M.S.)--University of Kentucky, 2002.
Title from document title page. Document formatted into pages; contains x, 84 p. : ill. Includes abstract. Includes bibliographical references (p. 76-82).

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.
Includes bibliographical references (p. 39-43).
A novel processing method was developed for sub-50 nm structures by integrating quantum dots (QDs) on patterned polymer substrates. Poly(styrene-alt-maleic anhydride) (PSMa) was prepared by the initiated chemical vapor deposition (iCVD) method, an alternative to spin-on deposition. The sub-50 nm PSMa polymer patterns were prepared by low energy oxygen plasma etching by using CNTs as the masks. The water soluble, amine-functionalized QDs underwent the nucleophilic acyl substitution reaction with the PSMa containing anhydride functional groups. This integration method is use to incorporate high performance QDs on inexpensive, lightweight flexible substrate.
by Chia-Hua Lee.
S.M.

Yes
Owing to their small size, good wettability, uniform dispersion ability and high thermal properties, the nickel-plated carbon nanotubes (Ni-CNTs) with different aspect ratios are used to reinforce reactive powder concrete (RPC) through modifying the nano/micro- structural units of concrete. Incorporating only 0.075 vol% of Ni-CNTs (0.03 vol% of CNTs) can significantly increase mechanical properties of RPC. The enhancement effect on compressive strength caused by the incorporation of Ni-CNTs with aspect ratio of 1000 reaches 26.8%/23.0 MPa, mainly benefiting from the high polymerization C-S-H gels, low porosity, and refined pore structure. The 33.5%/1.92 MPa increases of flexural strength can be attributed to the decrease of large pore, original cracks, molar ratio of CaO to SiO2, and gel water content when Ni-CNTs with aspect ratio of 125 are added. Ni-CNTs with aspect ratio of 1500 have the largest utilization rate of being pulled-out, resulting from the improvement of dispersibility and the pining effect of nickel coating and then leading to the increased toughness. Therefore, incorporating Ni-CNTs can fundamentally modify the nano/micro- scale structural nature of RPC, providing a bottom-up approach for controlling the properties of RPC.
Funding supported from the National Science Foundation of China (51908103 and 51978127) and the China Postdoctoral Science Foundation (2019M651116).
The full-text of this article will be released for public view at the end of the publisher embargo on 7th Dec 2021.

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).

In this thesis, we develop approaches for carrying out inference and model-based experimental design, under both internal and external sources of uncertainty. Specifically, in Chapter 1, we develop a stochastic growth model for the carbon-based super material, Graphene, and propose approaches for relating controllable experimental factors to the underlying growth mechanism. In Chapter 2 we develop a unified framework for carrying out response surface optimization when the input factors are noisy, and in Chapter 3, we explore the problem of designing optimal experiments, under the extra uncertainty generated by noisy inputs. Internal noise, a term used to describe the phenomenon of noisy inputs, is found to adversely affect optimization and model-based optimal designs. We show that accounting for this internal noise during the design and modeling stages significantly improve inference. In particular, we develop a modified optimality criterion for generating optimal experimental data, and show improvements in subsequent inference based on that data. In Chapter 4, a missing data perspective is used to improve inference on deformations along the profile of 3D printed products. We show that these deformations depend on missing angles, which can be used to infer global and local deformation patterns. We use the inferred deformation model to design compensation plans for minimizing deformations on future printed objects.
Statistics

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 revolution of electronic devices has shown substantial enhancement in terms of functionality, structure and higher efficiency over the last few decades. One recent approach is the replacement of the most fundamental component of the electronic device with carbon nanostructures. The unique properties of carbon-based nanostructures make them widely used in many fields ranging from material science, energy and environment, biology and medicine. In this PhD thesis, we theoretically investigate and identify, through accurate quantum mechanical first-principles calculations, promising carbon-based structures for applications in the nano-technology industry such as molecular-devices, semiconductors, and superconductors. The Density Functional Theory (DFT) approach will be used as it is the most widely employed and successful method to solve the Schrödinger equation for the quantum mechanical description of the atomic structures. We apply DFT with self-consistent non-equilibrium Green’s function (NEGF) to model the conductance of azulene quinone derivatives which are placed between semi-infinite gold electrodes which allows experimentalists to synthesis and design unprecedented molecular devices constituted of such non-alternant hydrocarbons for moletronics applications. From molectronics to twistronics, we explored the electronic and transport characteristics of twisted hetero bilayer graphene/phosphorene systems with such features could have an impact on enhancing the applications of two-dimensional twisted structures in nano electronics. Subsequently, we have shown how graphene and/or boron-nitride can maintain a crucial role in protecting a well-known two-dimensional superconductor, magnesium diboride, while maintaining its electronic properties. Finally, we investigate how both monolayers phosphorene and molybdenum disulfide have high potential gas-sensing capabilities for Hydrogen Peroxide because detecting such a cancerous molecule with real-time and cost-effective two-dimensional electrochemical sensors, would highly benefit in early diagnosis required for efficient treatment. All studies undertaken will yield not only a better understanding of the properties and applications of carbon-based nano-electronic devices, but also the prediction and identification of new promising device materials and structures.

Planar two-dimensional (2-D) nanostructured indium oxide (InOx) and one-dimensional (1-D) tin oxide (SnO2) semiconductor metal-oxide layers have been utilised for gas sensing applications. Novel layered Surface Acoustic Wave (SAW) based sensors were developed consisting of InOx/SiOxNy/36°YXLiTaO3, InOx/SiNx/SiO2/36°YXLiTaO3 and InOx/SiNx/36°YXLiTaO3 The 1 µm intermediate layers of silicon oxynitride (SiOxNy), silicon nitride (SiNx) and SiO2/SiNx matrix were deposited on lithium tantalate (36°YXLiTaO3) substrates by r.f. magnetron sputtering, electron-beam evaporation and plasma enhanced chemical vapour deposition (PECVD) techniques, respectively. As a gas sensitive layer, a 100 nm thin layer of InOx was deposited on the intermediate layers by r.f. magnetron sputtering. The targeted gases were ozone (O3) and hydrogen (H2). An intermediate layer has multiple functions: protective role for the interdigital transducers' electrodes as well as an isolating effect from InOx sensing layer, thereby improving the sensor performance. The developed SAW sensors' exhibited high response magnitudes with repeatable, reversible and stable responses towards O3 and H2. They are capable of sensing concentrations as low as 20 parts-per-billion for O3 and 600 parts-per-million for H2. Additionally a conductometric type novel sensing structure of SnO2/36°YX LiTaO3 was also developed by depositing a thin layer of SnO2 nanorods by PECVD. The gas sensing performance exhibited repeatable, reversible, stable responses towards NO2 and CO. The surface morphology, crystalline structure and preferred orientation of the deposited layers were investigated by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). A polycrystalline, oxygen deficient non-stoichiometric InOx with grain sizes of 20-40 nm was revealed. The 1-D nanostructures were characterised by Transmission Electron Microscopy (TEM) showing nanorods with needle-like shape , diameters of 10-20 nm a t the top and 30-40 nm at the base as well as a preferential growth orientation of [ ] on the LiTaO3 substrate. The developed sensors are promising for O3, H2 and CO sensing.

Carbon nanotubes (CNTs) have been assessed for their use in electrochemical energy storage applications, namely Hydrogen Storage and Vanadium Redox Flow Batteries. Furthermore;fundamental electrochemical studies have been conducted on aligned arrays of carbon nanotubes, and for the first time electrochemistry on pure, defect free, single layer graphene is reported. CNTs have been assessed for their potential as an electrochemical hydrogen storage material,finding a maximum recorded capacity for a single walled nanotube sample (SWNT) that was comparable to literature gas phase adsorption values. In-situ Raman spectroelectrochemistry was used to probe structural changes of the SWNTs with applied potential: no chemical functionalisation of the tubes or intercalation of protons was observed. It was concluded, therefore, that CNTs present no unique electrochemical hydrogen storage ability, other than their role as an adsorbent for gaseous hydrogen, which was evolved electrochemically. CNTs were also assessed as a possible electrode material for the VO(2+)/VO2(+) reaction, used in the positive half cell of commercial vanadium redox flow batteries and widely reported to exhibit quasi-reversible kinetics on carbon electrodes. Initial investigations revealed apparently reversible kinetics using a SWNT, the first time such a response has been observed on Carbon, and in contradiction to published work using CNTs for this application. Analysis via a range of electrochemical techniques highlighted the difficulty in using cyclic voltammetry to assess reversibility, particularly for CNT modified electrodes. The system was subsequently found to be quasi-reversible, with the deceptively small peak separation inferred to arise from the pores of the CNT electrode, therefore thin layer cell behaviour was observed. The porous contribution was confirmed using an electrode exhibiting poor kinetics (very small, indistinct Faradaic peaks), increasing the electrode porosity (using an aligned array of CNT) had a remarkable effect, with large Faradaic peaks (low separation ˜ 0.02-0.04 V) observed for a sample that was chemically identical. This work highlights the fundamental error in a portion of CNT literature, where kinetic enhancement is quantified by voltammetric peak separation, which can be erroneous unless the inherent porosity of the electrodes is considered. In contrast to the complexity of CNTs, graphene represents an ideal electrode material, allowing for direct determination of the electrochemical response of the graphene basal plane, eliminating the contribution of edge sites. An initial investigation towards this goal is presented.

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.

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

There is an every increasing need to develop more durable and higher performing coatings for use in a range of products including tools, devices and bio-implants. Nano-structured coatings either in the form of a nanocomposite or a multilayer is of considerable interest since they often exhibit outstanding properties. The objective of this thesis was to use advanced plasma synthesis methods to produce novel nano-structured coatings with enhanced properties. Coatings consisting of combinations of aluminum (Al), aluminum nitride (AlN) and amorphous carbon (a-C) were investigated. Cathodic vacuum arc deposition and unbalanced magnetron sputtering were used to prepare the coatings. By varying the deposition conditions such as substrate bias and temperature, coatings with a variety of microstructures were formed. A comprehensive range of analytical methods have been employed to investigate the stoichiometry and microstructure of the coatings. These include Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), Electron Energy Loss Spectroscopy, Auger Electron Spectroscopy, X-ray diffraction and Raman spectroscopy. In addition to the investigation of microstructure, the physical properties of the coatings were measured. Residual stress has been recognized as an important property in the study of thin film coatings since it can greatly affect the quality of the coatings. For this reason, residual stress has been extensively studied here. Hardness measurements were performed using a nano indentation system, which is sensitive to the mechanical properties of thin films. This thesis undertook the most comprehensive investigation of the Al/AlN multilayer system. A major finding was the identification of the conditions under which layers or nanocomposite form in this system. A model was developed based on energetics and diffusion limited aggregation that is consistent with the experimental data. Multilayers of a-C and Al were also found to form nanocomposites. No hardness enhancement as a function of layer thickness or feature size was observed in either the Al/AlN or a-C/a-C systems. It was found that the most important factor which determines hardness is the intrinsic stress, with films of high compressive stress exhibiting the highest hardness. Nano-structured multilayers of alternating high and low density a-C were investigated. For a-C multilayers prepared using two levels of DC bias, evidence of ion beam induced damage was observed at the interfaces of both the low and high density layers. In addition, the structure of the high density (ta-C, known as tetrahedral amorphous carbon) layers was found to be largely unchanged by annealing. These results extend our understanding of how a-C form from energetic ion beams and confirms the thermal stability of ta-C in a multilayer. This thesis also presented the first attempt to synthesis a-C multilayered films with a continuously varying DC bias in sinusoidal pattern. The resulting films were shown to have a structurally graded interface between layers and verified that ion energy and stress are the most important factors which determine the structure of a-C films.

Oxygen reduction reaction (ORR) catalysts are of crucial importance in developing low- and medium-temperature fuel cells, as PEMFCs (Polymer Electrolyte Membrane Fuel Cells), from which sizeable energy saving and reduction of greenhouse gas emission are expected in comparison with the use of coal and oil based fuels in thermal engines. The same electrochemical oxygen reduction reaction takes place in oxygen depolarized cathodes (ODC) in chlor-alkali electrolysis, replacing the conventional hydrogen evolving cathode, gaining about 30% energy consumption reduction in the overall process. At present carbon-supported Pt and Pt-rich alloys are best credited to the ORR purpose. However, Pt-based catalysts are not free from certain drawbacks, such as oxide formation and Pt particle coarsening through Ostwald ripening, that decrease the overall cell energy conversion efficiency. Furthermore, attendant problems concerning natural availability, geographic distribution and cost of platinum, render platinum supply strategic and fuel cells hardly scalable to mass production. At present, projections on platinum usage for PEMFCs are estimated at ~15 ton y-1 in addition to the current ones, at a cost of ~40 $ g-1. Therefore, non-precious metal catalysts are actively searched for, such as to meet already established operational benchmarks for conventional platinum PEMFC vehicular requirements (0.5 W cm-2; 5500 h durability) with the additional target of significant cost reduction. Several papers on non-precious ORR catalysts have been published after a first report by Jasinski in 1964 demonstrating the ORR activity of metal substitutes-phthalocyanines. Then, research on metal-nitrogen macrocycles significantly expanded, leading to the picture that ORR catalytic activity can be related to N4-Me and N2-Me moieties. However, for precursors cost and unsatisfactory lifetime performance, research was steered toward more simple nitrogen-containing reactants and preparation procedures. Significant steps in this direction were obtained by Dodelet et al. who demonstrated that ORR overpotentials almost linearly decrease with increasing nitrogen content in carbon. Positive results were obtained on a series of samples prepared by high temperature treatment of carbon precursors in NH3/H2/N2 mixtures; doping of these modified carbons with iron rather than cobalt salts was shown to be preferable for better efficiency in oxygen reduction, even though still lower than that of platinum. Further improvements both in terms of incipient ORR potentials and currents were obtained by Maruyama et al. using carbons from hemoglobin and adenine-glucose pyrolysis in the presence of added Fe(II) and Cu(II)/Fe(II) mixtures, respectively. The ORR promoting role of nitrogen in carbon was independently demonstrated both theoretically and experimentally. Indeed, it was found that substitutional nitrogen at a few, specific, peripheral positions of graphene layers in well-ordered carbon nanostructures is in itself able to promote ORR activity even in the absence of accompanying metal centers. Besides the above examined composition-dependent factors, catalyst activity also depends on structural and morphological carbon support features. In fact, many electrocatalytic reactions show faster kinetics on carbon edge planes compared with basal ones. This is related to the ability of the edges to more readily chemisorb O2 (this is the same reason why O2 combusts faster from edges and defects). On the other hand, an optimized porosity of carbon supports is beneficial for an easy access of the oxygen to the catalyst layer in contact with the proton exchange electrolyte membrane. Despite carbon materials of different textural morphology are widely used at an industrial level as supports for precious metal catalysts, in the PEMFC field, electrocatalysts are by far supported on the same VULCAN XC72 carbon. Given that improved catalytic activity of Pt-based catalysts has been achieved by the use of carbons with pore size centered in the mesoporous region, even developed with advanced synthesis, including template methods, such strategy should be pursued also for Pt-free catalytic systems. In this project a number of Pt-free N-doped C-based catalysts have been synthesized on the basis of different synthetic and templating strategies aiming to understand how compositional, morphological and textural aspects of the end material can affect the electrochemical behaviour of ORR. Materials have been characterized using different physico-chemical methods including a study of the kinetics and mechanism of the electrochemical oxygen reduction reaction. Electrochemical results were obtained by rotating disk electrode (RDE) and rotating ring disk electrode (RRDE). Surface and bulk analyses have been performed by BET technique, XPS and XRPD (sometimes data were recorded at synchrotron facilities). (HR) TEM, SEM (combined with FIB milling) imaging was also performed to characterize samples morphology. Many types of samples have been synthesized, starting with mesoporours N-, Fe- doped carbons obtained by heat treatment of a solution of precursors, using silica as a templating agent. Outstanding results in terms of ORR electroactivity in acidic and alkaline conditions have been recorded. Some samples, especially in alkaline media, catalyze ORR even better than commercial Pt-based catalysts. Then, attempting to prepare materials with a precise and defined order and trying to emphasize some of their properties such as surface area and conductivity, ordered carbonaceous nano- and microstructures were synthesized. By chemical vapor deposition N-, Fe- doped carbon nanotubes (N-CNTs) were prepared and some interesting aspects related to the aging of the Fe-doped MgO catalyst used to grow N-CNTs were evidenced. Then, a modified method, but very similar to that used in the synthesis of nanotubes, surprisingly allowed the synthesis of innovative N-doped hollow carbon nanocubes (N-CNCs). This is the great novelty of the work. Due to nanocubes endothermal transformation, happening at 37°C, as detected by DSC, and to the empty space available in the internal part of each cube, many applications can be thought for example involving cubes as nano-reactors that can be opened/close in correspondence of body’s temperature changes. This feature could be taken into considerations for medical applications, after testing and verifying the biocompatibility of nanocubes. Finally, a completely different technique, an ultraspray pyrolysis method (USP) was used to obtain N-, Fe- doped carbon microspheres. The inherent scalability of continuous flow methods such as USP represents a significant advantage compared to alternative synthetic strategies requiring batch processing or surface catalyzed deposition of nanostructured carbon materials (e.g. CVD growth), this feature might be useful in order to improve electrode packing and, consequently, mass transport electrocatalytic applications. The last results section, apparently diverging from the main goals of the present work, was thought to better understand the electronic C-surface behavior in charge transfer reactions. This is actually strongly connected to the oxygen reduction reaction, for which all the catalysts, hereby synthesized, were designed. However, instead of starting from complicated systems involving porous and doped-carbons, the choice was addressed to the simplest but closest material: annealed and non-annealed amorphous carbon thin films prepared by DC-magnetron sputtering technique. Part of the work described was carried out at Trinity College Dublin in the laboratory of Prof. Colavita as a part of an academic collaboration and 5 months exchange granted by the European LLP Erasmus Program.

Interest in high performance portable energy devices for electronics and electric vehicles is the basis for a significant level of activity in battery research in recent history. Li-ion batteries are of particular interest due to their high energy density, decreasing cost, and adaptable form factor. A common goal of researchers is to develop new materials that will lower the cost and weight of Li-ion batteries while simultaneously improving the performance. There are several approaches to facilitate improved battery system-level performance including, but not limited to, the development of new material structures and/or chemistries, manufacturing techniques, and cell management. The performed research sought to enhance the understanding of structure-property relationships of carbon-containing composite anode materials in a Li-ion cell through extensive materials and anode performance characterization. The approach was to focus on the development of new electrode material designs to yield higher energy and power characteristics, as well as increased thermal and electrical conductivities or mechanical strength, using techniques that could be scaled for large volume manufacturing. Here, three different electrode architectures of nanomaterial composites were synthesized and characterized. Each electrode structure consisted of a carbon substrate that was conformally coated with a high Li capacity material. The dimensionality and design for each structure was unique, with each offering different advantages. The addition of an external coating to further increase the stability of high capacity materials was also investigated.

Incorporation of conductive carbon fillers into polymer matrices can improve electrical,thermal and mechanical properties of the resulting composites. In this work, three differentconductive carbon fillers were used; i.e. graphite, graphite nanoplatelets (GNP) and asreceivedmultiwall carbon nanotubes (A-MWCNT). In addition, A-MWCNT were modifiedusing mixed acids and named as T-MWCNT. These four fillers were incorporated into poly(ethylene terephthalate) (PET) to prepare four types of PET/carbon micro- and nanocomposites. These composites were prepared by melt compounding using a Haake Minilabextruder equipped with a co-rotating twin screws. The extruded samples were compressionmoulded to films of 1 mm thickness and were subsequently quenched to obtain lowcrystallinity samples. The extruded samples were also injection moulded to obtain dumbbellshaped specimens. The electrical, morphological, thermal and mechanical properties of thesecomposites were studied and characterized as a function of carbon filler types and contentsusing a wide range of analytical and testing techniques: namely; impedance spectroscopy,DSC, TGA, SEM, TEM, FTIR, DMTA and tensile testing. The results demonstrated that theaddition of graphite, GNP and A-MWCNT produced electrically conductive composites andthat the conductivities were found to be dependent on several factors; including filler type,filler content and processing conditions. The PET/A-MWCNT nanocomposites showed anexcellent electrical conductivity (~ 0.2 S/m at 2 wt. % A-MWCNT) with a low percolationthreshold (Fc ~ 0.33 wt. %). In contrast, PET/T-MWCNT nanocomposites displayed similarelectrical conductivity to that of pure PET and no percolation threshold was observed in thiscase (until 2 wt. % of CNT), this was attributed to the acid treatment which disrupted theinherent electrical conductivity of the CNT and also reduced their aspect ratio. However, TMWCNTshowed better dispersion and distribution into the PET matrix as well as reducedCNT-CNT interactions and therefore do not as readily form network structures. This resultedin better mechanical properties in comparison to the PET/A-MWCNT nanocomposites. Interms of processing, increasing screw speed during mixing was found to enhance theelectrical conductivities of PET/carbon nanocomposites (GNP and A-MWCNT), but onlyabove the percolation thresholds values, by ~ 2 – 3 orders of magnitude. However, nosignificant change was observed in the electrical conductivities of PET/graphitemicrocomposites. All the carbon fillers, with different dimensions, were found to act asnucleating agents for the PET matrix and hence accelerated crystallization and increased thedegree of crystallinity. CNT were found to accelerate the crystallization at lower loadingscompared to GNP and graphite. In addition, it was found that quenched PET and compositesamples were not fully crystallized after processing and therefore (cold) crystallized duringthe first heating cycle in both DSC and DMTA, as indicated by crystallisation peaks duringthe DSC first-heat and a rise in storage moduli above Tg during the DMTA first heat. Ingeneral, TGA showed that carbon fillers improved the resistance to thermal and thermooxidativedegradation under both air and nitrogen atmospheres. However, a reduction inthermal stability was observed for the composites containing T-MWCNT in air. The carbonfillers increased the storage and tensile moduli of the composites compared to pure PET.However; tensile strength and elongation at break were reduced except for compositecontaining T-MWCNT which showed no significant change at lower loadings. The tensile23moduli of nanocomposites were predicted using Halpin-Tsai models, which showed goodagreement at low loadings of A-MWCNT (≤ 0.2 wt. %) and GNP (≤ 2 wt. %). However,poor agreement was observed at higher loadings of fillers where the composites displayedreduced reinforcement efficiency. This correlates with results from SEM, which showedagglomeration, poorer distribution, debonding and rolling up of fillers in the PET matrix athigher loadings.

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.

Thesis (Ph. D.)--Textile and Fiber Engineering, Georgia Institute of Technology, 2007.
Committee Chair: Kumar, Satish; Committee Member: Carr, Wallace; Committee Member: Graham, Samuel; Committee Member: Griffin, Anselm; Committee Member: Yao, Donggang.

La Synthèse Fischer-Tropsch (SFT) est une technologie clé pour transformer le gaz de synthèse (CO + 2H2) en hydrocarbures liquides, matières premières pour la chimie de base. Il s'avère que les catalyseurs à base de cobalt sont les plus performants et leur développement dans l'industrie impose au matériau support de posséder une conductivité thermique élevée et une structure ouverte. Dans ce travail, un nouveau support hiérarchisé constituée deα -Al2O3, recouvert homogènement de nanotubes de carbone, a été préparé pour supporter des catalyseurs au cobalt. Ces derniers montrent une très grande sélectivité en hydrocarbures liquides ainsi que de meilleures activités catalytiques. Les performances obtenus ont pu être améliorées en déposant une fine couche de TiO2 sur la surface des nanotubes de carbone, améliorant considérablement la dispersion du cobalt et l'activité. Le TiO2, également introduit dans la matrice de β-SiC lors de la synthèse, interagit fortement avec les sites actifs de cobalt, conduisant ainsi à sa grande dispersion et à une meilleure activité et stabilité dans la réaction de SFT. Parallèlement, un catalyseur à base de β-SiC de haute porosité, recouvert d'une couche de dioxyde de titane monocristallin a été développé et testé. Un taux spécifique de 1,2 gC5+. gcat -1. h-1 et une sélectivité en C5+ de 86% ont été obtenus. Ces performances sont les plus élevées signalées jusqu'à présent sur des catalyseurs sans cobalt
The Fischer-Tropsch synthesis (FTS) is a key technology to transform the synthesis gas (2H2 + CO) into liquid hydrocarbons as the basic chemical feedstock. It can be found that the cobalt active sites supported on the materials with high thermal conductivity, opened structure is necessary to accelerate FTS synthesis process in the development of industry catalysts.In this work, a new hierarchical support consisting of α-Al2O3, which is homogeneously covered by a layer of carbon nanotubes, is successfully prepared to support cobalt catalyst. The supported cobalt catalysts show extremely high selectivity towards liquid hydrocarbons along with the better catalytic activity. The FTS performance obtained on this support can be further improved by coating a thin layer of TiO2 on the CNTs surface which significantly improve the cobalt dispersion and in turn,the FTS activity.The TiO2 is also successfully introduced into the matrix of β-SiC during the synthesis process which strongly interacts with cobalt active sites, leading to high dispersion of cobalt, accounting for the better activity and stability in FTS reaction. In the mean time, a highly activity Fischer-Tropsch catalyst based on single crystalline titanium dioxide coated high porosity β-SiC was also developed. The FT specific rate of 1.2 gC5+·gcat -1·h-1 and a C5+ selectivity of 86 % are obtained,which are among the highest FT performance reported up to now on cobalt noble-free catalyst

Ce travail de thèse est consacré à l'étude sur une large gamme de températures d'un système unidimensionnel modèle, les nano-peapods de carbone. Ces composés sont constitués de fullerènes (C60, dans notre cas) insérés dans des nanotubes de carbone monofeuillets. Les diamètres des fullerènes et des tubes étant concordant, les fullerènes s'arrangent selon un réseau 1D.Dans le premier chapitre de ce manuscrit, nous décrivons la synthèse des peapods de carbone. Dans les deux chapitres suivants, nous décrivons les différents modèles et méthodes expérimentales qui nous permettent de déterminer l'évolution de la structure moyenne des chaînes de fullerènes, ainsi que la dynamique de rotation et de translation des molécules.Dans les trois derniers chapitres, nous décrivons l'évolution de la structure et de la dynamique des chaînes sur trois gammes de températures, que nous appelons hautes (500-1100 K), basses (0-200 K), et intermédiaires (200-500 K). Les résultats expérimentaux concernant deux types d'échantillons, les peapods monomères et les peapods polymères (dans lesquels les degrés de liberté de rotation sont restreints) sont confrontés à des modèles analytiques. Nous mettons en évidence trois comportements différents des chaînes dans ces trois gammes de température.

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 project is focused on the synthesis, modification and characterization of rhodium based catalysts supported on MCM-41 mesoporous silica to produce well-defined active sites for catalysis of CO oxidation at low-temperature. The Rh catalysts were prepared by incipient wetness impregnation (IWI) then modified by the inclusion of different transition metal oxides (ca. CeOx, ZrOx, CrOx, Ce0.5Zr0.5Ox and Ce0.5Cr0.5Ox) via two different routes. The first was achieved by pre-modification of MCM-41 support during its synthesis using the inorganic precursors of the promoter oxides followed by the addition of the specified Rh precursor (0.5 - 2.5 wt%), i.e. post-synthesis of Rh catalysts. The second route was performed by the post addition of the promoters using their non-inorganic sources [ca. Ce(acac)3, Zr(acac)4 and bis(benzene)chromium] by the controlled surface modification (CSM) method. The catalysts were characterized by using TGA, FT-IR, N2 physisorption analysis, PXD, SEM-EDX, TEM, DR UV/Vis spectroscopy and XPS. Furthermore, the structure-performance relationship and the dependence of the preparation method towards CO oxidation were also investigated by in situ QEXAFS-MS spectroscopy in the temperature range of 300 - 573 K. The combination of soft and hard X-ray absorption edges was applied to in situ structural studies. In addition to the Rh K-edge, the Ce L3, Zr K or Cr K-edges were used as probes of the catalysts as a function of temperature (300 - 573 K) under of different ambient gases (He, 10% H2/He, 10% O2/He and 10% CO/O2/He) during activation and reaction conditions. As a result, the fractions of Rh active species, coordination numbers and atom-to-atom distances were extracted from analysis of XANES and EXAFS results. In addition, the turnover frequency (TOF) values and CO conversion% over these catalysts were also calculated. The results revealed that Rh species and/or the promoter oxides prepared by both two methods were well confined into the mesoporous framework of silica support in amorphous nano-sized scale. However, the distribution of the Rh atoms and/or the promoter oxides depends mainly on the preparation method with much more homogeneity and local vicinity in those prepared by the CSM method. Furthermore, the preparation method played a crucial rule not only in the local structure, but also in the catalysts performance towards CO oxidation with high activity for catalysts prepared by CSM.

Les propriétés exceptionnelles des nanotubes de carbone (CNT) attirent de nombreux industriels dans les domaines de la microélectronique, des matériaux ou de la nanomédecine. Néanmoins, le risque sanitaire lié à ce nanomatériau reste encore mal compris. Des profils toxicologiques différents, dépendant des caractéristiques physico-Chimiques des CNT, ont été mis en évidence. Une approche « safer by design » est proposée, afin d’identifier les paramètres pouvant, dès la conception des CNT, pour limiter le risque sanitaire. Dans ce contexte, cette thèse avait pour objectif d’étudier l’impact sur la réponse in vitro d’une lignée de macrophages murins (RAW 264.7) de deux traitements de post-Production de CNT : la fonctionnalisation acide et le recuit haute température.Les groupements acides en surface des CNT fonctionnalisés ont entrainé une augmentation de la réponse pro-Inflammatoire sans influencer significativement la cytotoxicité. D’un autre côté, la fonctionnalisation acide, principalement par l’élimination des impuretés métalliques, a permis de diminuer le stress oxydant. Les CNT recuits à haute température étaient à l’origine d’une réponse pro-Inflammatoire plus importante que les CNT bruts, confirmant lasensibilité de cette réponse biologique à la chimie de surface. En revanche, le recuit n’a pas diminué significativement le stress oxydant malgré la purification des CNT, suggérant l’importance des défauts de structure sur cette réponse biologique. La fonctionnalisation acide de nano-Graphite et de noir de carbone a eu un impact similaire à celle des CNT sur l’activité biologique des macrophages. La comparaison de ces trois nanomatériaux fonctionnalisés semble s’accorder avec le paradigme mettant en exergue la toxicité spécifique des fibres et des plaquettes. Enfin, afin de compléter ces résultats, des études exploratoires sur les interférences entre les tests de toxicité et les CNT, ainsi que sur le stress oxydant, ont été conduites
Due to their exceptional properties, carbon nanotubes (CNT) have aroused a huge interest among in industrial fields such as microelectronics, material science and nanomedicine. Nevertheless, the health impacts of this nanomaterial still remain not well understood. The first toxicological studies pointed out that there is no unique response regarding the healthimpact of the CNT, but different toxicological profiles according to their various physicochemical properties. A safer by design approach is thus proposed to identify the parameters decreasing from their production the CNT biological impacts. In this context, this work aimed at studying the impact on the in vitro response from a macrophage cell line (RAW 264.7) of two post-Production treatments: acid functionalization and high temperature annealing.Surface acid groups from functionalized CNT enhanced the pro-Inflammatory response although the cytotoxicity remained stable. On the other hand, acid functionalization, through the elimination of metallic impurities, significantly decreased the oxidative stress. Annealed CNT increased the pro-Inflammatory response compared to the pristine CNT. It thus confirmed the sensitivity of this response for the changes in surface chemistry. However, the high temperature annealing did not influence the oxidative stress, despite of the CNT purification. It suggested that structural defects are also of importance for this response. Besides, the acid functionalization of nano-Graphite and carbon black displayed trends in the macrophage response similar to the acid functionalization of CNT. The comparison of these three carbon-Based nanomaterials seemed to conform to the fibre and platelets paradigm. Eventually, exploratory studies have also been conducted on the interferences between CNT and the toxicity assays, and on the oxidative stress

La dispersion des nanotubes de carbone (NTC) dans le polyfluorure de vinylidène (PVDF) est un grand défi pour avoir de meilleures propriétés diélectriques. Les hybrides, titanate de baryum (BT)-NTC, ayant une structure particulière sont révélés être efficaces pour l'amélioration de la dispersion de NTC dans la matrice de polymère et la réduction du seuil de percolation du matériau composite. Cette thèse vise à atteindre une haute performance diélectrique du composite via la conception de charges ayant une structure favorable ainsi que l'étude exhaustive de l'interaction entre les NTC et la matrice de polymère semi-cristallin.Dans le chapitre 1, un bref revu de l'état de l'art sur le contexte général des matériaux diélectrique est introduite ainsi les progrès récents dans ce domaine sont présentés pour mieux comprendre les composites et leurs application.Dans le chapitre 2, nous préparons deux types d'hybrides avec deux structures différentes. Les premiers hybrides sont préparés par un dépôt chimique en phase vapeur (CVD). Les BT forment le noyau de ces hybrides et les NTC croient dessus (H-NTC-BT). Les deuxième hybrides sont préparées par réaction hydrothermale où NTC sont revêtus par les BT (H-BT-NTC). Par la suite, nous préparons des composites avec une matrice de PVDF renforcés par les deux types d'hybrides déjà synthétisés cela en coulant la solution puis par extrusion-injection. En outre, les méthodes de caractérisation de la morphologie, des propriétés thermiques, diélectriques et la cristallisation sont également introduites dans ce chapitre.Dans le chapitre 3, les comportements diélectriques de H-NTC-BT/PVDF sont étudiés en détails. Une augmentation dramatique de la permittivité diélectrique est observée après le traitement thermique. Ce changement peut être dû à la réorganisation du réseau conducteur de NTC et la recristallisation de PVDF. Par la modélisation et la caractérisation expérimentale, Nous déduisons que cette augmentation significative de la permittivité diélectrique après le traitement thermique est dû au rétrécissement de la distance de NTC dans des couches amorphes voisine de PVDF d'un côte et au polymorphe β à l'interface NTC-PVDF d'un autre.Dans le chapitre 4, la dispersion des NTC dans la matrice du composite PVDF est étudiée par la conception de différentes structures. Tout d'abord, une comparaison du seuil de percolation de H-NTC-BT/PVDF calculé et celui déterminé expérimentalement est menée pour mieux comprendre la morphologie de H-NTC-BT. Ensuite, deux comparaisons sont menées:- La première compare les facteurs de transformation de la dispersion des NTC dans les composites H-NTC-BT/PVDF et NTC/PVDF cela en mesurant de la conductivité AC dans les différentes couches de ces composites.- La deuxième compare trois types de composites de PVDF renforcés par des hybrides ayant la même fraction volumique de NTC et BT mais des structures différentes. L'effet de ces différentes structures de ces hybrides est étudié en comparant leurs propriétés diélectriques.Pour finir une conclusion générale est présentée dans le chapitre 5 ainsi les perspectives prévues pour les travaux futurs
The dispersibility of carbon nanotube (CNT) in polyvinylidene fluoride (PVDF) is always a big challenge for the high dielectric property. Barium titanate (BT)-CNT hybrids with the special structure are proved to be effective for improving the dispersion of CNT in the polymer matrix and reduce the percolation threshold of the composite. This thesis aims to achieve high dielectric performance of composites via designing fillers with the favorable structure as well as comprehensively study the interaction between CNT and semi-crystalline polymer matrix.In chapter 1, we provide a general introduction about dielectric material's background knowledge. Meanwhile the development including recent breakthroughs and their applications for the dielectric field are also provided in this chapter.In chapter 2, we prepare two hybrids with different structures. The first hybrids are prepared by chemical vapor deposition (CVD) method. It is with the structure of BT as a core and CNTs growing outsides (H-CNT-BT). The second hybrids are prepared by hydrothermal reaction where BT particles coats outside CNT (H-BT-CNT). Meanwhile, we fabricate hybrids reinforced PVDF matrix composites by solution casting plus extrusion-injection way. Additionally, methods for characterization involving morphology, thermal and dielectric properties as well as crystallization are also introduced in this chapter.In chapter 3, the dielectric behaviors of H-CNT-BT/PVDF are studied concretely. A dramatic increment on dielectric permittivity is observed after the thermal treatment. This change may result from the reformation of CNT's conductive network and the behavior of PVDF's re-crystallization. By modeling work and experimental characterization, the shrinkage of the neighboring CNT's distance in PVDF's amorphous layers and the induced β polymorph at the CNT-PVDF interface may cause the significant increment in dielectric permittivity after the thermal treatment.In chapter 4, the CNT's dispersibility in PVDF matrix composites is studied by designing different structures. Firstly, a comparison between calculated and experimental percolation threshold of H-CNT-BT/PVDF is conducted for studying the morphology parameters of H-CNT-BT. Afterwards, two comparisons are conducted: one is between H-CNT-BT/PVDF and CNT/PVDF. The processing factors for the CNT's dispersibility are discussed via measuring the different layer's AC conductivity. The other is among three hybrids reinforced PVDF composites. The hybrids structure's effect the CNT's dispersibility is discussed via comparing the dielectric property of the composites with the same volume fraction of CNT and BT but different structures.In chapter 5, a general conclusion is formed according to the works and the perspective is provided for the improvement of the future work

Electrocatalysis is key to both sensitive electrochemical sensing and efficient electrochemical energy conversion. Despite high catalytic activity, traditional metal catalysts have poor stability, low selectivity, and high cost. Metal-free, carbon-based materials are emerging as alternatives to metal-based catalysts because of their attractive features including natural abundance, environmental friendliness, high electrical conductivity, and large surface area. Altering surface functionalities and heteroatom doping are effective ways to promote catalytic performance of carbon-based catalysts. The first chapter of this dissertation focuses on developing electrode modification methods for electrochemical sensing of biomolecules. After electrochemical pretreatment, glassy carbon demonstrates impressive figures-of-merit in detecting small, redox-active biomolecules such as DNA bases and neurotransmitters. The results highlight a simplified surface modification procedure for producing efficient and highly selective electrocatalysts. The next four chapters focus on evaluating nitrogen-doped carbon nano-onions (𝑛-CNOs) as electrocatalysts for oxygen reduction and CO2 reduction. 𝑛-CNOs exhibit excellent electrocatalytic performance toward O2 to H2O reduction, which is a pivotal process in fuel cells. 𝑛-CNOs demonstrate excellent resistance against CO poisoning and long-term stability compared to state-of-the-art Pt/C catalysts. In CO2 electrochemical conversion, 𝑛-CNOs demonstrate significant improvement in catalytic performance toward reduction of CO2 to CO with a low overpotential and high selectivity. The outstanding catalytic performance of 𝑛-CNOs originates from the asymmetric charge distribution and creation of catalytic sites during incorporation of nitrogen atoms. High contents of pyridinic and graphitic N are critical for high catalytic performance. This work suggests that carbon-based materials can be outstanding alternatives to traditional metal-based electrocatalysts when their microstructures and surface chemistries are properly tailored.

The first study researched turbulent forced convective heat (mass) transfer down- stream of blockages with round and elongated holes in a rectangular channel. The blockages and the channel had the same cross section, and a distance equal to twice the channel height separated consecutive blockages. Naphthalene sublimation experiments were conducted with four hole aspect ratios (hole-width-to-height ratios) and two hole-to-blockage area ratios (ratios of total hole cross-sectional area to blockage area). The effects of the hole aspect ratio, for each hole-to-blockage area ratio, on the local heat (mass) transfer distribution on the exposed primary channel wall between consecutive blockages were examined. Results showed that the blockages with holes enhanced the average heat (mass) transfer by up to 8.5 and 7.0 times that for fully developed turbulent flow through a smooth channel at the same mass flow rate, respectively, in the smaller and larger hole-to-blockage area ratio (or smaller and larger hole diameter) cases. The elongated holes caused a higher average heat (mass) transfer and a larger spanwise variation of the local heat (mass) transfer on the channel wall than did the round holes. The second study explored the heat transfer enhancement for pool boiling on nano-structured surfaces. Experiments were conducted with three horizontal silicon surfaces, two of which were coated with vertically aligned multi-walled carbon nanotubes (MWCNT) with heights of 9 and 25 ¹m, respectively, and diameters between 8 and 15 nm. The MWCNT arrays were synthesized on the two silicon wafers using chemical vapor deposition. Experimental results were obtained over the nucleate boiling and film boiling regimes under saturated and sub-cooled (5±C and 10±C) boiling conditions. PF-5060 was the test fluid. Results showed that the MWCNT array with a height of 25 ¹m enhanced the nucleate and film boiling heat fluxes on the silicon surface by up to 380% and 60%, respectively, under saturated boiling conditions, and by up to 300% and 80%, respectively, under 10±C sub-cooled boiling conditions, over corresponding heat fluxes on a smooth silicon surface. The MWCNT array with a height of 9 ¹m enhanced the nucleate boiling heat flux as much as the taller array, but did not significantly enhance the wall heat flux in the film boiling regime.

The outstanding properties of carbon nanotubes (CNTs) keep attracting the attention of researchers from different fields. CNTs are promising candidates for applications e.g. in lightweight construction but also in electronics, medicine and many more. The basis for the realization of the manifold applications is a detailed knowledge of the material properties of the carbon nanotubes. In particular for applications in lightweight constructions or in composites, the knowledge of the mechanical behavior of the CNTs is of vital interest. Hence, a lot of effort is put into the experimental and theoretical determination of the mechanical material properties of CNTs. Due to their small size, special techniques have to be applied. In this research, a modified molecular structural mechanics model for the numerical determination of the mechanical behavior of carbon nanotubes is presented. It uses an advanced approach for the geometrical representation of the CNT structure while the covalent bonds in the CNTs are represented by beam elements. Furthermore, the model is specifically designed to overcome major drawbacks in existing molecular structural mechanics models. This includes energetic consistency with the underlying chemical force field. The model is developed further to enable the application of a more advanced chemical force field representation. The developed model is able to predict, inter alia, the lateral and radial stiffness properties of the CNTs. The results for the lateral stiffness are given and discussed in order to emphasize the progress made with the presented approach.

Les travaux menés dans le cadre de cette thèse sont focalisés sur les procédés deréplication permettant la transformation des mélanges en composants par les technologiesen séquentiel ou bien en continu, selon les applications visées. Les développementsconcernent la mise en place et l’hybridation de différents procédés de micro-réplication(estampage à chaud de polymère thermoplastique et par laminage circulaire entre deuxrouleaux). Ces deux procédés sont développés et optimisés pour l’élaboration decomposants micro-structurés ou de microcomposants possédant des propriétésfonctionnelles mécaniques ou thermo-physiques requises à partir de différents mélangeschargés en poudres métalliques ou en nanotubes de carbone. Des exemples de réalisationde composants structurés, à base d’un système micro-fluidique possédant plusieurs canauxde 200 microns par 200 microns et des réservoirs de diamètre de 2 mm, sont prises commeexemple tout au long de ces travaux de cette thèse. Différents travaux de caractérisationsont été entrepris pour optimiser les procédés de micro-réplication par estampage à chaud etpar laminage circulaire entre deux rouleaux
The Ph.D subject concerns the study of two micro-replication processes by hotembossing and roll to roll processes for thermoplastic polymers and loaded polymers withpowders or carbon nanotubes. The micro-replication processes, realized in sequential orcontinuous ways, use some different elaborated loaded feedstocks in order to obtainstructural components or micro-component with high aspect ratio and mechanical orthermo-physical properties.A chain combining hot embossing and roll embossing and powder metallurgy have beendeveloped in our lab and investigated. The different micro mould die cavities have beenrealized with different micro-manufacturing process, elastomeric mould has been obtainedby casting process. Finally, a metallic structured die cavity has been obtained by combininghot embossing and debinding and sintering stages. The second topic is the comparison ofmetallic die cavity mould obtained by roll embossing or rolls embossing. Two demonstratorshave been developed during the preparation of this Ph.D period: first a metallic micro-fluidicsystem with micro-structuration with diameter of 1 mm for the reservoir and 200 microns by200 microns for the channel have been realized and characterized by different methods.Secondly, some functional micro-component has been obtained with carbon nanotube andsome specific properties in terms of mechanic and thermo-physical properties have beencharacterized

Des nano-objets hybrides organiques-inorganiques formés par assemblages électrostatiques de nanoparticules minérales, de nanotubes de carbone et de polymères/oligomères en volume et à une interface sont étudiés dans ce travail de thèse. En fonction de la nature des briques/composants élémentaires, différents types de complexes sont générés : nano-colloïdes singulets stables, coacervats cœurs-écorces, agrégats fractals et tubes décorés. Ces objets possèdent des propriétés de volume et de surface intéressantes ce qui leur permet d’être utilisés pour générer des interfaces fonctionnelles. L’influence du procédé de mise œuvre sur leur nanostructure et leur morphologie finale est étudié dans un deuxième temps ; la possibilité de développer des morphologies diverses à partir d’un nombre limité de composés chimiques différents est également souligné. Finalement, une nouvelle méthode de croissance de couches hétéro-structurées à partir d’une interface solide/liquide est décrite ; certains mécanismes de croissance sont proposés ; le potentiel de cette approche dans le domaine de la fonctionnalisation de surface est discuté au travers d’exemples

Isolante. On a étudié les processus de formation d'une structure ségrégée, qui conduisait à la formation d'une distribution ordonnée de particules dans une matrice polymère. Il est montré que dans le système ségrégé, la valeur du seuil de percolation φc est d'un ordre de grandeur inférieur à celui d'un composite présentant une distribution aléatoire des charge (2,95% vol. pour le composite ségrégé contre 24,8% vol. pour le composite à distribution aléatoire). Le seuil de percolation dans le cas d'un mélange de charges est très inférieur à la valeur calculée à l'aide de la règle des mélanges. Il est montré que les résultats expérimentaux de conductivité thermique ne révèlent pas de comportement de percolation et peuvent être décrits de façon satisfaisante par le modèle de Lichtenecker. La valeur du paramètre λf traduisant la conductivité thermique de la charge en tenant compte de l’interface charge/matrice est de 4,4 fois plus élevé pour les systèmes ségrégés que pour un composite à distribution aléatoire de particules. Il est montré que dans les systèmes ségrégés, les paramètres de blindage sont considérablement augmentés en raison de l'absorption provoquée par la réflexion interne sur les parois conductrices du réseau de charges conductrices. Il est établi que les charges de carbone constituent la base la plus efficace, ce qui garantit une absorption élevée des rayonnements électromagnétiques (REM) aux faibles concentrations. Il est avéré que le plus grand effet de blindage est observé pour un mélange de charges hybrides GNP/CNT (nanoplaques en graphite / nanotubes de carbone). L'effet de synergie s'explique par la meilleure interaction du REM avec le réseau hybride ramifiée formés par les charges, ce qui entraîne une absorption accrue du REM. Les systèmes à structure ségrégée à base d'élastomères présentent un effet piézorésistif prononcé avec une relation linéaire de déformation / modification de l'intensité du courant. L'étude de l'effet piézorésistif dans une large gamme de température (-40 / +50°С) a montré la stabilité des caractéristiques principales et la possibilité d'utiliser le composite dans une large gamme de températures
The thesis determines the principles of the conductive phase structure formation in polymer composites containing conductive fillers, which will be different types of carbon fillers. The processes of segregated structure formation in which the particles of the filler are localized on the surfaces of polymer grains is studied. It is shown that the value of the percolation threshold φc for the segregated system is one order lower than in the composite with a random distribution of the filler 2.95 vol.% and 24.8 vol.%, respectively. The hybrid filler shows percolation threshold, much lower than the value calculated using the mixing rule. Experimental results of thermal conductivity for systems filled with anthracite, graphene and hybrid filler Gr/A do not reveal percolation behaviour and can be well described by the Lichtenecker model. It is shown that λf for segregated systems is 4.4 times higher than for a composite with a random distribution of filler particles. It is shown that in segregated systems the shielding parameters are significantly increased due to the absorption caused by the internal reflection on the conductive walls of the filler framework. Carbon fillers create the most effective basis that ensures a high absorption rate of EMI at low concentrations. It was found that the greatest shielding effect in the interaction of a composite with electromagnetic radiation was observed for the hybrid filler GNP/CNT (graphite nanoplatelets/carbon nanotubes). The synergistic effect is explained not by their higher electrical conductivity, but by the better interaction of the EMI with the developed hybrid framework of the filler, which causes increased absorption of the EMI. Systems with a segregated structure based on elastomer (ground rubber) with a polymer-adhesive and hybrid electroconductive nano-fillers exhibit a significant piezoresistive effect. The cyclic studies of electric response, depending on the applied external load, showed a linear relationship between composite deformation and current changes through the sample and demonstrate stable long-term stability. The study of the piezoresistive effect in a wide temperature range (-40 ÷ +50°C) showed the stability of the main characteristics and the possibility of exploiting the composite in a wide temperature range

碩士
崑山科技大學
機械工程研究所
102
This study aimed at investigating the synthesis of carbon nanostructures in butanol/aqueous ammonia and ethanol/aqueous ammonia flames using an alcohol lamp burner. Pure n-butanol (purity 99.8%), pure ethanol (purity 95%), n-butanol/aqueous ammonia (25% NH3) blends, and ethanol/aqueous ammonia blends were used in this study. Aqueous ammonia was mixed with various proportions (10, 20, and 30%) in butanol or ethanol for use as liquid fuels. A nascent nickel mesh was employed as the catalytic metal substrate to collect deposit materials. The deposition time was two minutes. Additionally, scanning electron microscope (FE-SEM) and high resolution field emission scanning transmission electron microscopy (HR-TEM) were used to observe and analyze the microstructure and morphology of generated carbon nonostructures under different experimental conditions. First, flame appearances were observed. With increasing the content of aqueous ammonia, it was found that the blue part generated at the yellow flame base became more apparent for the n-butanol/aqueous ammonia flames, and that the flame color changed gradually from yellow to brown for the ethanol/aqueous ammonia blends. From the results of SEM analysis, it was observed that, for pure n-butanol, carbon nanotubes (CNTs) were synthesized at the axial positions z = 6, 8, 10 and 12 mm above the wick where the temperature was in the range of about 700 – 950℃. As n-butanol concentration was 90% in the n-butanol/aqueous ammonia blends, carbon nano-onions (CNOs) were produced at the heights z = 10, 12, 14, 16, 18, 20 and 22 mm where the temperature was between 750 and 950℃. For the n-butanol concentration of 80%, CNTs were fabricateded at a lower axial position z = 4 mm, where the temperature was identified to lie between 700 and 740℃; however, at higher heights z = 12, 14, 16, 18, 20 and 22 mm, CNOs were synthesized, where the temperature was located in the range of 825 – 1030℃. As the n-butanol concentration was 70%, CNTs were found at lower hights z = 4 and 6 mm where the temperature range was within 620 – 750℃; however, at higher heights z = 12, 14, 16, 18 and 20 mm with a temperature range of about 800 – 1040℃, CNOs were observed. For pure ethanol (100% ethanol), at the height z = 4 and 6 mm (where the temperature range was about 520 – 620 ℃), CNTs were generated. For the ethanol concentration of 90%, at the heights z = 4, 6 and 8 mm (where the temperature was ranged approximately from 750 to 850 ℃), CNTs were synthesized. Under the operating conditions of ethanol concentration being 80%, at the heights z = 4, 6 and 8 mm (where a temperature range of about 690 – 780 ℃ was generated), CNTs were produced. As ethanol concentration was 70%, at the heights z = 4 and 6 mm (where the temperature range was about 655 – 770 ℃, few CNTs were fabricated; whereas, at the heights z = 8, 10, 12, 14 and 16 mm (where the temperature range of about 840 – 1030 ℃ was produced), more CNTs were synthesized. With increasing axial position from z = 8 mm progressively, a larger amount of CNTs were synthesized at z = 8 mm, achieved the maximum yield at z = 10 mm afterwards, and then the formation of CNTs decreased gradually. Based on the results of HR-TEM analysis, it is noteworthy that few layer graphenes were also observed (which were not found easily in SEM analysis) when the concentration of n-butanol was 100% and the sampling positions were located at z = 10 and 12 mm or when the concentration of n-butanol was 90% and the sampling positions were placed at z = 14 and 18 mm. Moreover, graphenes were not observed in pure ethanol and ethanol/aqueous ammonia flames.

碩士
崑山科技大學
機械工程研究所
98
Combustion synthesis of carbon nano-structures using ethylene-air partially-premixed jet flames and a catalytic Ni substrate was investigated. In the experiments, the injection velocity of fuel-air mixture was kept constant. The influences of sampling position, gas temperature and concentration distributions on the synthesis of carbon nanostructures were examined. The results showed that the increase of fuel concentration leads to an increase of flame height and a wider range of yellow flame (sooty zone). Additionally, a quantity of carbon nano-onions was synthesized at Z = 40 ~ 60 mm for ethylene concentrations of 15.1%, 15.7% and 16.3%; however, only little carbon nanostructure was synthesized at Z = 70 mm because the temperature was too high. It has been verified that the key parameters influencing the formation and yield of CNOs were carbon sources (mainly both the CO and C2H2 concentrations), and heat source (suitable temperature range around 970 ~ 1300 ℃). High-resolution transmission electron microscopy (HR-TEM) and scanning electron microscopy (SEM) images confirmed the presence of spherical carbon nano-onions with diameters ranging from 20 to 40 nm.

碩士
崑山科技大學
機械工程研究所
100
Methane jet diffusion flames modulated by acoustically excitation in an atmospheric environment were used to synthesize carbon nano- structures. A catalytic nickel substrate was employed to collect the deposit materials at sampling positions z = 10 mm above the burner exit. The influence of acoustic amplitude and frequency on flame synthesis of carbon nanotubes (CNTs) and nano-onions (CNOs) was investigated. The formation of CNOs was significantly enhanced by acoustic excitation at the frequencies near either the natural flickering frequency (ƒN = 20 Hz) or the acoustically resonant frequency (ƒR = 90 Hz). At these characteristic (resonant) frequencies, flow mixing was markedly enhanced by acoustic excitation, and the flame structure with a bright slender core flame was generated, which provided a favorable flame environment, i.e. a high radical concentration (carbon source) and a temperature range (heat source), for the formation of CNOs. The power of the acoustic exciter, P, (related to the amplitude of the excitation) was adjustable. At P = 5W, the production rate of CNOs was high at 20 Hz (near the natural flickering frequency) for a sampling position z = 10 mm above the burner exit where the gas temperature was about 660℃. Additionally, a quantity of CNTs could be obtained at 70 ~ 95 Hz, near the acoustically resonant frequency, where the gas temperature was between 660~870℃. However, almost no CNOs and CNTs were synthesized for the other frequencies due to low temperature or lack of carbon sources. At higher power of the acoustic exciter, P = 10 and 15W, a mass of CNTs could be fabricated at 70 ~ 85 Hz, close to the acoustically resonant frequency, where the gas temperature was in the range of 660~810℃. On the contrary, nearly no carbon nano-material was observed for the other frequencies due to low temperature or lack of carbon source. Finally, Raman spectra showed that the intensity ratios of the D- and G-bands for all the carbon nano-structures synthesized herein were lower than one (i.e. ID/IG < 1). This reveals that the CNTs and CNOs had a high degree of graphitization. The enhanced synthesis of CNOs was caused by strong mixing of the fuel and oxidizer due to the acoustic excitation at the resonant frequencies.

The objective of the present work is to finite element (FE) modelling and analysis of different nanocomposite structures such as airfoil and parabolic antenna for free vibration analysis (to find the different modal natural frequencies and mode shapes) as well as forced vibration analysis (to obtain the equivalent von Mises stresses and maximum transverse displacements). The analysis is done for Carbon Nanotube reinforced Composites with varying percentage of carbon nanotube content. First the mathematical model on Carbon Nanotube reinforced Composite was used to find out the different properties; i.e. Young's Modulus, Bulk modulus and so on with different volume fraction of Carbon Nanotube content present. Next step is to model the structures; i.e. airfoil and parabolic antenna by solid modelling and then covert it into Finite Element model by giving the proper meshing, conditions and input data. The FE model was then analysed with the help of ANSYS and the different mode shapes and fundamental vibration frequencies were found. The some important results were then presented into a table for comparison and discussion.

碩士
崑山科技大學
機械工程研究所
102
Methane jet diffusion flames modulated by acoustically excitation in an atmospheric environment were used to synthesize carbon nano- structures. A catalytic nickel substrate was employed to collect the deposit materials at sampling positions z = 10 and 15 mm above the burner exit. The influence of acoustic amplitude and frequency on flame synthesis of carbon nanotubes (CNTs) and nano-onions (CNOs) was investigated. The formation of CNOs was significantly enhanced by acoustic excitation at the frequency near the natural flickering frequency (ƒN = 20 Hz), and the fabrication of CNTs was greatly enhanced by acoustic excitation at the acoustically resonant frequency (ƒR = 90 Hz). At these characteristic (resonant) frequencies, flow mixing was markedly enhanced by acoustic excitation, and the flame structure with a bright slender core flame was generated, which provided a favorable flame environment, i.e. a high radical concentration (carbon source) and a temperature range (heat source), for the formation of CNOs or CNTs. The power of the acoustic exciter, P, related to the amplitude of the excitation, was adjustable. At P = 5, 10, and 15 W, the production rate of CNOs was high at 20 Hz (near the natural flickering frequency) for a sampling position z = 10 mm above the burner exit where the gas temperature was about 450~550℃. Additionally, a quantity of CNTs could be obtained at 80 ~ 95 Hz, near the acoustically resonant frequency, where the gas temperature was between 700 and 740℃. However, almost no CNOs and CNTs were synthesized for the other frequencies due to low temperature or lack of carbon sources. The enhanced synthesis of CNOs was caused by strong mixing of the fuel and oxidizer due to the acoustic excitation at the resonant frequencies. For fixed acoustic amplitude 10W and fuel velocity V = 20 cm/s,the results of concentration field analysis showed that at low frequencies and low C2H2 concentrations, a lot of carbon nano-onions were synthesized; but at high frequencies and high C2H2 concentrations, carbon nanotubes were fabricated.

碩士
崑山科技大學
機械工程研究所
95
The formation and growth of carbon nano-structures including carbon nanotubes (CNTs) and carbon nanocapsules in inverse co-flowing diffusion flames of mixed fuel were experimentally studied. The influences of volumetric methane concentrations in ethylene/nitrogen mixture from the outer jet, sampling position and substrate (uncoated or coated with Ni(NO3)2-36.4% by weight) upon the yield of carbon nano-structures were particularly emphasized. The flame appearance, flame structure, and flame stability under the influences of inner/outer velocity ratios, volumetric oxygen concentrations in nitrogen of the inner jet and methane concentrations in ethylene/nitrogen mixture of the outer jet were firstly studied using image processing techniques. The results showed that increasing the injection velocity of oxygen/nitrogen mixture, the sooty zone becomes narrower, leading to an increase in the critical methane concentration require for the occurrence of yellow flame (sooty zone). However, raising oxygen concentration of inner jet or fuel (methane or ethylene) concentration of outer jet resulted in an increase in flame height and a wider range of sooty zone, and in turn a decrease in the critical fuel concentration required for the occurrence of yellow flame. Thereafter, we employed a sampling Ni grid as the catalytic metal substrate for the carbon nano-structures growth. The sampler was mounted on a two-dimensional micro-positioner with the plane normal to the burner axis. The sampling time of the substrate inside the flame was kept at 120 sec. The SEM and TEM images showed that carbon nano-structures depositted on the substrates were mainly CNTs and carbon nanocapsule. Curved and entangled tubular multi-walled CNTs (MWCNTs) were harvested, which had both typical straight tubular and bamboo-like structures. Besides curved CNTs, carbon nanocapsules were also synthesized, inside which metal particles were encapsulated. It is of interest to note that only MWCNTs were generated when the mixture of 5% methane/5% ethylene/90% nitrogen and the mixture of 10% methane/5% ethylene/85% nitrogen were separately used as the fuel. Both the growth range and yield of CNTs of the former are smaller than those of the latter. However, carbon nanocapsules synthesized on Ni(NO3)2-coated substrates were found when the methane concentration of outer fuel jet was equal to 30% (i.e. 30% methane/5% ethylene/65% nitrogen). Furthermore, for the same sampling approach, the sampling positions on or near the flame front had a greater carbon nano-structures harvest than those far from the flame front. Using Ni(NO3)2-coated substrates had advantages over uncoated Ni(NO3)2 substrates, which can increase the range, quantity and length of carbon nano-structures.