Dissertations / Theses on the topic 'METALLIC CARBON NANOTUBES'

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.
Includes bibliographical references (p. 101-108).
Metallic carbon nanotubes are one dimensional conductors that are both technologically promising for electronic applications, and scientifically interesting for studying the physics of low dimensional materials. In this thesis, we present a detailed study of the inelastic light scattering (Raman) spectrum of individual metallic carbon nanotubes, with a focus on the influence of electronic excitations and charged carriers. We have demonstrated that the frequency and linewidth of certain phonon modes of metallic carbon nanotubes depend strongly the Fermi energy, because they couple strongly to low lying electron hole pairs. Next, we report the first experimental observation of electronic Raman scattering in carbon nanotubes. This observation demonstrates that the same electron-hole pairs that participate in damping the optical phonons of metallic carbon nanotubes, may themselves scatter light, thus giving rise to an electronic Raman spectrum. An analysis of the Fermi level and laser energy dependence of the electronic Raman and phonon Raman contributions allows us to explain the asymmetric lineshape of the G-band phonon modes in terms of a Fano interference. In another experiment, we have shown that the charge-induced expansion and contraction of the the graphitic C-C bond length is different for metallic and semiconducting nanotubes. Finally, we have measured the Stokes and antiStokes intensities of the Raman modes in electrically contacted metallic nanotubes in order to determine their phonon populations during high-field electrical transport. The experiments reported here, have helped to clarify the origin of several features in the Raman spectra of metallic carbon nanotubes that have been heavily debated in recent years. These result also shed light on the way electronic excitations and charged carriers affect the physical properties of metallic carbon nanotubes.
by Hootan Farhat.
Ph.D.

Single-wall carbon nanotubes (SWCNTs) are a fascinating material because they exhibit many outstanding properties. Due to their unique geometric structure, they are a paradigm for one-dimensional systems. Furthermore, depending on their chirality, they can be either metallic or semiconducting. The SWCNT are arranged in bundles of some ten nanotubes with a random distribution of semiconducting and metallic tubes. They are thus one-dimensional objects embedded in a three-dimensional arrangement, the bundles. In this thesis, the metallic ground state of one-dimensional (1D) and three-dimensional (3D) systems is investigated on the basis of SWCNTs, using angle-integrated photoemission spectroscopy. In particular, a transition from a 1D to a 3D metallic system, induced by a charge transfer, is studied on SWCNTs and C60 peapods. In general, the metallic ground state of materials is greatly influenced by correlation effects. In classical three-dimensional metals, electron-electron interaction mainly leads to a renormalization of the charge carrier properties (e.g. effective mass), as described in Landau's Fermi liquid theory. One-dimensional metals are influenced to a greater extent by interactions. In fact, the Landau-quasiparticle picture breaks down due to the Peierls instability. Instead, one-dimensional metals are described by Tomonaga-Luttinger liquid (TLL) theory which predicts unusual properties such as spin-charge separation and non-universal power laws in some physical properties such as the electronic density of states (DOS). Angle-integrated photoemission spectroscopy provides direct access to the DOS and as such directly addresses the power law renormalization of a TLL. It is first shown, that the bundles of single-wall carbon nanotubes indeed exhibit a power law scaling of the electronic density of states is observed as it is expected from TLL theory. The main part of the thesis is devoted to the investigation of the metallic ground state of SWCNTs upon functionalization. In general, functionalization is a controlled modification of the structural and/or electronic properties of SWCNT. It can be carried out e.g. by doping with electron donors or acceptors, by filling the nanospace inside the tubes with molecules or by substituting carbon atoms. First, the behavior of the SWCNT upon chemical doping was probed. The overall modification of the electronic band structure can be explained well by a rigid band shift model. The one-dimensional character of the metallic tubes in the bundle is retained at low doping, but when the semiconducting tubes in the sample are also rendered metallic by the charge transfer, a Fermi edge emerges out of the power law renormalization of the spectral weight, signifying a transition to a three-dimensional metallic behavior. This can be explained by an increased interaction between the tubes in the bundle. A crossover from a Tomonaga-Luttinger liquid to a Fermi liquid is observed. The filling of SWCNTs with C60 molecules leads to the formation of so-called peapods. It raises questions concerning the role of the additional bands originating from the C60 filling in the one-dimensional system. In the pristine state, the states of the C60 filling were found to have no influence on the metallic ground state. The TLL power law scaling of the density of states is observed. The overall interaction between the SWCNT host and the C60 filling is small. Upon doping however, the modified band structure leads to a qualitative change in the crossover from a TLL to a Fermi liquid. Upon doping, also states in the conduction band of the C60 are filled. The evolution of the power law scaling at intermediate doping can be interpreted as an opening of an additional conduction channel of one-dimensional metallic chains of C60 inside the tubes. This is in good agreement with transport experiments. Upon further doping, a Fermi edge similar to the highly doped SWCNTs is observed.

Single-wall carbon nanotubes (SWCNTs) are a fascinating material because they exhibit many outstanding properties. Due to their unique geometric structure, they are a paradigm for one-dimensional systems. Furthermore, depending on their chirality, they can be either metallic or semiconducting. The SWCNT are arranged in bundles of some ten nanotubes with a random distribution of semiconducting and metallic tubes. They are thus one-dimensional objects embedded in a three-dimensional arrangement, the bundles. In this thesis, the metallic ground state of one-dimensional (1D) and three-dimensional (3D) systems is investigated on the basis of SWCNTs, using angle-integrated photoemission spectroscopy. In particular, a transition from a 1D to a 3D metallic system, induced by a charge transfer, is studied on SWCNTs and C60 peapods. In general, the metallic ground state of materials is greatly influenced by correlation effects. In classical three-dimensional metals, electron-electron interaction mainly leads to a renormalization of the charge carrier properties (e.g. effective mass), as described in Landau's Fermi liquid theory. One-dimensional metals are influenced to a greater extent by interactions. In fact, the Landau-quasiparticle picture breaks down due to the Peierls instability. Instead, one-dimensional metals are described by Tomonaga-Luttinger liquid (TLL) theory which predicts unusual properties such as spin-charge separation and non-universal power laws in some physical properties such as the electronic density of states (DOS). Angle-integrated photoemission spectroscopy provides direct access to the DOS and as such directly addresses the power law renormalization of a TLL. It is first shown, that the bundles of single-wall carbon nanotubes indeed exhibit a power law scaling of the electronic density of states is observed as it is expected from TLL theory. The main part of the thesis is devoted to the investigation of the metallic ground state of SWCNTs upon functionalization. In general, functionalization is a controlled modification of the structural and/or electronic properties of SWCNT. It can be carried out e.g. by doping with electron donors or acceptors, by filling the nanospace inside the tubes with molecules or by substituting carbon atoms. First, the behavior of the SWCNT upon chemical doping was probed. The overall modification of the electronic band structure can be explained well by a rigid band shift model. The one-dimensional character of the metallic tubes in the bundle is retained at low doping, but when the semiconducting tubes in the sample are also rendered metallic by the charge transfer, a Fermi edge emerges out of the power law renormalization of the spectral weight, signifying a transition to a three-dimensional metallic behavior. This can be explained by an increased interaction between the tubes in the bundle. A crossover from a Tomonaga-Luttinger liquid to a Fermi liquid is observed. The filling of SWCNTs with C60 molecules leads to the formation of so-called peapods. It raises questions concerning the role of the additional bands originating from the C60 filling in the one-dimensional system. In the pristine state, the states of the C60 filling were found to have no influence on the metallic ground state. The TLL power law scaling of the density of states is observed. The overall interaction between the SWCNT host and the C60 filling is small. Upon doping however, the modified band structure leads to a qualitative change in the crossover from a TLL to a Fermi liquid. Upon doping, also states in the conduction band of the C60 are filled. The evolution of the power law scaling at intermediate doping can be interpreted as an opening of an additional conduction channel of one-dimensional metallic chains of C60 inside the tubes. This is in good agreement with transport experiments. Upon further doping, a Fermi edge similar to the highly doped SWCNTs is observed.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2003.
Includes bibliographical references.
Carbon nanotubes are a remarkable material with many appealing properties. Despite the appeal of this material, there are few synthesis techniques capable of producing nanotubes in large quantities at low-cost. The broad objective of this study was to examine the potential of a premixed flame for the synthesis of carbon nanotubes with the view that flame synthesis may prove a means of continuous production at low-cost. The specific approach focused on the formation of metallic nanoparticles in flames; identification of nanotube formation zones, time scales, and transition conditions; characterization of material properties; and the development of a formation mechanism and associated flame-model. Carbon nanotube formation requires a source of carbon, a source of heat and the presence of metal particles. A fuel-rich flame is a high-temperature, carbon-rich environment and addition of metal is likely to give conditions suitable for nanotube growth. This study considered a premixed acetylene/oxygen/15 mol% argon flame doped with iron pentacarbonyl (Fe(CO)₅) vapor (typically 6100 ppm), operated at 50 Torr pressure and 30 cm/s cold gas feed velocity. The flame was investigated with regard to the growth of metal particles and subsequent formation and growth of carbon nanotubes. Thermophoretic samples were extracted from the flame at various heights above burner (HAB) and analyzed using transmission electron microscopy (TEM). HAB is representative of residence time in the flame. Size distribution and number density data were extracted from TEM images using a quantitative image analysis technique. The mean particle size for a precursor concentration of 6100 ppm was observed to increase from around 2 to 4 nm between 20 and 75 mm HAB.
(cont.) The particle number density results showed a decreasing number density with increasing HAB, giving a complementary picture of the particle dynamics in the flame. Single-walled carbon nanotubes (SWNT) were also observed to form in the premixed flame. Thermophoretic sampling and TEM analysis gave insight into nanotube formation dynamics. Nanotube structures were observed to form as early as 30 mm HAB (20 ms) with growth proceeding rapidly within the next 10 to 20 mm HAB. The growth-rate for the nanotubes in this interval is estimated to be between 10 and 100 ptm per second. The upper region of the flame (50 to 70 mm HAB; 35 to 53 ms) is dominated by tangled web structures formed via the coalescence of individual nanotubes formed earlier in the flame. The nanotube structures are exclusively single-walled with no multi-walled nanotubes observed in any of the flame samples. The effect of carbon availability on nanotube formation was tested by collecting samples over a range of fuel equivalence ratios at fixed HAB. The morphology of the collected material revealed a nanotube formation 'window' of 1.5 < < 1.9, with lower dominated by discrete particles and higher favoring soot-like structures. These results were also verified using Raman spectroscopy. A clear trend of improved nanotube quality (number and length of nanotubes) is observed at lower . More filaments were observed with increasing concentration, however the length (and quality) of the nanotubes appeared higher at lower concentrations ...
by Murray John Height.
Ph.D.

The continuous migration to smaller feature sizes puts high demands on materials and technologies for future ultra-large-scale integrated circuits. Particularly, the copper-based interconnect system will reach fundamental limits soon. Their outstanding properties make metallic carbon nanotubes (CNTs) an ideal material to partially replace copper in future interconnect architectures. Here, a low contact resistance to existing metal lines is crucial. The present thesis contributes to the theory and numerical description of electronic transport in metallic CNTs with metal contacts. Different theoretical approaches are applied to various contact models and electrode materials (Al, Cu, Pd, Ag, Pt, Au) are compared. Ballistic transport calculations are based on the non-equilibrium Greens function formalism combined with tight-binding (TB), extended Hückel theory (EHT) and density functional theory (DFT). Simplified contact models allow a qualitative investigation of both the influence of geometry and CNT length, and the strength and extent of the contact on the transport properties. In addition, such simple contact models are used to compare the influence of different electronic structure methods on transport. It is found that the semiempirical TB and EHT are inadequate to quantitatively reproduce the DFT-based results. Based on this observation, an improved set of Hückel parameters is developed, which remedies this insufficiency. A systematic investigation of different contact materials is carried out using well defined atomistic metal-CNT-metal structures, optimized in a systematic way. Analytical models for the CNT-metal interaction are proposed. Based on that, electronic transport calculations are carried out, which can be extended to large systems by applying the computationally cheap improved EHT. The metal-CNT-metal systems can then be ranked by average conductance: Ag ≤ Au < Cu < Pt ≤ Pd < Al. This corresponds qualitatively with calculated contact distances, binding energies and work functions of CNTs and metals. To gain a deeper understanding of the transport properties, the electronic structure of the metal-CNT-metal systems and their respective parts is analyzed in detail. Here, the energy resolved local density of states is a valuable tool to investigate the CNT-metal interaction and its influences on the transport
Die kontinuierliche Verkleinerung der Strukturgrößen stellt hohe Anforderungen an Materialen und Technologien zukünftiger hochintegrierter Schaltkreise. Insbesondere die Leistungsfähigkeit kupferbasierte Leitbahnsystem wird bald an fundamentale Grenzen stoßen. Aufgrund ihrer hervorragenden Eigenschaften könnten metallische Kohlenstoffnanoröhren (engl. Carbon Nanotubes, CNTs) Kupfer in zukünftigen Leitbahnsystemen teilweise ersetzen. Dabei ist ein geringer Kontaktwiderstand mit vorhandenen Leitbahnen von entscheidender Bedeutung. Die vorliegende Arbeit liefert grundlegende Beiträge zur Theorie und zur numerischen Beschreibung elektronischer Transporteigenschaften metallischer CNTs mit Metallkontakten. Dazu werden verschiedene theoretische Ansätze auf diverse Kontaktmodelle angewandt und eine Auswahl von Elektrodenmaterialen (Al, Cu, Pd, Ag, Pt, Au) verglichen. Die Beschreibung ballistischen Elektronentransports erfolgt mittels des Formalismus der Nichtgleichgewichts-Green-Funktionen in Kombination mit Tight-Binding (TB), erweiterter Hückel-Theorie (EHT) und Dichtefunktionaltheorie (DFT). Vereinfachte Kontaktmodelle dienen der qualitativen Untersuchung des Einflusses von Geometrie und Länge der Nanoröhren, sowie von Stärke und Ausdehnung des Kontaktes. Darüber hinaus erlauben solch einfache Modelle mit geringem numerischen Aufwand den Einfluss verschiedener Elektronenstrukturmethoden zu untersuchen. Es zeigt sich, dass die semiempirischen Methoden TB und EHT nicht in der Lage sind die Ergebnisse der DFT quantitativ zu reproduzieren. Ausgehend von diesen Ergebnissen wird ein verbesserter Satz von Hückel-Parametern generiert, der diesen Mangel behebt. Die Untersuchung verschiedener Kontaktmaterialien erfolgt an wohldefinierten atomistischen Metall-CNT-Metall-Strukturen, welche systematisch optimiert werden. Analytische Modelle zur Beschreibung der CNT-Metall-Wechselwirkung werden vorgeschlagen. Darauf aufbauende Berechnungen der elektronischen Transporteigenschaften, können mit Hilfe der verbesserten EHT auf große Systeme ausgedehnt werden. Die Ergebnisse ermöglichen eine Reihung der Metall-CNT-Metall-Systeme hinsichtlich ihrer Leitfähigkeit: Ag ≤ Au < Cu < Pt ≤ Pd < Al. Dies korrespondiert qualitativ mit berechneten Kontaktabständen, Bindungsenergien und Austrittarbeiten der CNTs und Metalle. Zum tieferen Verständnis der Transporteigenschaften erfolgt eine detaillierte Analyse der elektronischen Struktur der Metall-CNT-Metall-Systeme und ihrer Teilsysteme. Dabei erweist sich die energieaufgelöste lokale Zustandsdichte als nützliches Werkzeug zur Visulisierung und zur Charakterisierung der Wechselwirkung zwischen CNT und Metall sowie deren Einfluss auf den Transport

Endohedral functionalization via supercritical CO2 was undertaken in order to produce encapsulation of organometallic systems that are difficult to encapsulate otherwise due to either their large size or extreme air sensitivity. Organometallic molecular systems from the prophyrin and phthalocyanine families (such as NiPc, ClAlPc and NiTPP) were successfully encapsulated inside of nanotubes with relatively large diameters (centred around 2 nm). This was assessed by a combination of high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. HRTEM revealed previously unreported ordering of NiTPP, a large planar molecule, in row-like assemblies inside nanotubes of diameters that match best the geometrical size of the molecule (2 nm), highlighting the role of confinement in promoting assembly. Using both endohedral and exohedral functionalization with NiTPP, ClAlPc and NiPc molecules provided a set of systems differing by only one specific parameter (e.g. central ion or body type, or size of the HOMO-LUMO gap), or comparatively affected the ability to bind to the nanotubes - the associated changes in the electronic properties of the nanotubes were revealed by resonant Raman spectroscopy. These changes were interpreted in terms of ability of the guest molecular species to produce charge transfer to/from the nanotube, and/or induce structural strain.

Recently, there has been a growing demand for electrode materials to serve as electrochemical capacitors (EC). It has been an important issue to come up with environment friendly electric power sources to reduce pollution caused by combustion engines of automotive systems. Even though conventional battery systems and fuel cells supply high energy, they lack the high specific power that would be required for hybrid power sources. The ECs can fill the gap between conventional capacitors and batteries.
Carbon nanotubes (CNTs), discovered by Iijima in 1991, attracted great attention in recent years for their unique properties, such as mesoporous character, excellent conductivity, moderate to high specific surface area as well as chemical and mechanical stability. These properties of CNTs make them useful in a wide of range applications including electrode materials for EC applications.
The preparation of CNT electrodes is accomplished by either pasting them onto metallic current collectors with the use of binder materials such as PVDF or growing them from deposited metal nanoparticles on substrates such as graphite paper. The deposition of metal nanoparticles is achieved via sputtering techniques or lengthy electrochemical deposition methods. The aim of this research was to simplify the preparation step by growing CNTs directly on metallic substrates and to study the relationship between surface area and electrochemical capacitance of CNTs. CNTs were produced on metal-alloy grids via chemical vapor deposition (CVD) of acetylene (C2H2). The physical characterization of the samples was achieved by Field Emission Scanning Electron Microscopy (FE-SEM), Raman spectroscopy and Single point BET surface area. The electrochemical performance of the samples was evaluated by cyclic voltammetry (CV) in a three electrode electrochemical cell with 1M sulfuric acid (H2SO4) solution as the electrolyte.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.
Includes bibliographical references (p. 117-125).
A double-walled carbon nanotube (DWNT) provides the simplest system to study the interaction between concentric tubes in carbon nanotubes. The inner and outer walls of a DWNT can be metallic (M) or semiconducting (S), and each of the four possible configurations (MUM, M©S, SUS, S©M) has different electronic properties. We analyze the Raman spectra from undoped and boron-doped chemical vapor deposition-derived DWNT bundles (CVD-DWNTs) that exhibit the "coalescence inducing mode" (CIM) as they are heat treated at temperatures between 12000C and 2000'C. We then report, for the first time, detailed Raman spectroscopy experiments carried out on individual DWNTs, where both concentric tubes of the same DWNT are measured under resonance conditions. A technique is developed that combines tunable Raman spectroscopy with Raman mapping procedures and electron beam lithography to enable the acquisition of Raman spectra from the individual constituents of the same isolated DWNT. By using the technique mentioned above, we measure resonant Raman scattering from 11 individual C60-derived double wall carbon nanotubes all having inner semiconducting (6,5) tubes and various outer metallic tubes. We report that in an individual DWNT an increase in the RBM frequency of the inner tube is related to an increase in the RBM frequency of the outer tube due to a decrease in the wall to wall distance. Finally, we use 40 laser excitation energies to analyze the differences in the Raman spectra from chemical vapor deposition-derived DWNT bundles (CVD-DWNTs), fullerene-derived DWNT bundles (C₆₀-DWNTs) and individual fullerene-derived DWNTs with inner type I and type II semiconducting tubes paired with outer metallic tubes.
by Federico Villalpando Páez.
Ph.D.

Orientador: Ana Flavia Nogueira
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-08-14T13:13:51Z (GMT). No. of bitstreams: 1 Conturbia_GiovannideLimaCabral_M.pdf: 7472586 bytes, checksum: 9ede857037431127443d2bed95bd1ccc (MD5) Previous issue date: 2009
Resumo:Células solares orgânicas têm despertado atenções devido ao baixo custo de produção e dos materiais utilizados, bem como devido à versatilidade química e de propriedades eletrônicas e ópticas dos semicondutores orgânicos. A eficiência atual atinge 5% (100 mWcm). Nanotubos de carbono encontram suas aplicações nessas células ora como eletrodos transparentes ora como material receptor de elétrons. Nesse trabalho, foi realizada a modificação química de nanotubos de carbono de única camada com grupos tióis, visando a incorporação de nanopartículas metálicas ou semicondutoras. O material de partida, bem como os nanotubos modificados, foi caracterizado por Espectroscopia Raman, Espectroscopia de Fotoelétron por Raios-X, Análise Térmica e Microscopia Eletrônica de Transmissão de Alta Resolução. Foi necessário um pós-tratamento (térmico e lavagens com diversos solventes) para que pudéssemos obter nanotubos individuais e funcionalizados. O pós-tratamento também possibilitou um aumento na fotocorrente dos dispositivos em comparação com o dispositivo sem nanotubos de carbono. A incorporação de nanopartículas de ouro no sistema P3HT/fulereno acresceu a fotocorrente e o fator de preenchimento dos dispositivos. Estudos de caracterização através de difração de raios-X, espectroscopia UV-visível e microscopia de força atômica, indicam que esse aumento está relacionado a uma mudança na morfologia do sistema, aumentando a cristalinidade do polímero e também ao efeito plasmônico com a adição das nanopartículas. Imagens de microscopia eletrônica de transmissão revelaram que as nanopartículas de ouro estão distribuídas tanto na fase polimérica quanto na fase contendo moléculas de fulereno
Abstract: Organic solar cells have attracted attention due to their low costs of production and materials used, as well as the chemical versatility and good electronic and optical properties of organic semiconductors. The current efficiency reaches 5% (100 mWcm). Carbon nanotubes materials can be applied in these cells as both transparent electrode or as electron acceptor materials. In this work, the chemical modification of single wall carbon nanotubes was carried out attaching thiol groups, aiming the incorporation of semiconductor or metallic nanoparticles. The raw material and the modified nanotubes were characterized by Raman Spectroscopy, X-ray Photoelectron Spectroscopy, Thermal Analysis and High Resolution Transmission Electron Microscopy. A post-treatment (thermal and washing with different solvents) was necessary in order to obtain single functionalized nanotubes. The post-treatment also allowed an increase in the photocurrent of the devices compared to the device without carbon nanotubes. The incorporation of gold nanoparticles in the P3HT/fullerene system increased the photocurrent and the fill factor of the devices. X-Ray diffraction, UV-vis Spectroscopy and Atomic Force Microscopy studies reveal that such increase can be related to the plasmonic effect and also to a change in the morphology, increasing polymer crystallinity after incorporation of the gold nanoparticles. High resolution transmission microscopy images showed that the nanoparticles are distributed between both polymer and fullerene phase.
Mestrado
Físico-Química
Mestre em Química

This thesis focuses on designing and synthesis of novel molecular imaging probes based on non-covalent funtionalisation of pure single-walled carbon nanotubes (SWNTs). Several synthetic strategies for the supramolecular chemistry functionalisation of SWNTs, cytotoxicity measurements and cellular imaging of supramolecularly functionalised carbon nanotube probes are discussed. Chapter one is a literature review as the thesis Introduction. This describes aspects of the physical and chemical properties, structural importance and synthesis methods of single-walled carbon nanotubes (SWNTs), also opens the discussion of the different functionalisation methods to enhance the solubility and biocompatibility of SWNTs for biomedical applications. Several approaches for the design of functionalisation SWNTs for molecular imaging reported in the current literature are highlighted. Techniques and facilities for accessing cell imaging ability and behavior of these synthesized molecular imaging probes, including confocal laser scanning microscopy (CLSM) and fluorescence-lifetime imaging microscopy (FLIM) are described briefly. Chapter two explores the synthesis of specifically designed naphthalene diimide (NDI). These molecules are known to form 3 dimensional (3D) helical organic nanotubes through hydrogen bonding. In this work an iodine-tagged NDI was allowed to self-assemble onto the surface of SWNTs. The cavities of the NDI organic nanotubes can accommodate SWNTs strands in their hydrophobic interior as observed high-resolution transmission electron microscopy (HR TEM). A new hybrid material, NDI@SWNT, was prepared and characterised as dispersed in organic solvents and aqueous media and in the solid state by HR TEM, tapping mode atomic force microscopy (TM AFM), scanning electron microscopy (SEM), circular dichroism, Raman and fluorescence spectroscopies (steady-state single and two-photon techniques). These measurements indicate that amino acid-functionalised NDI interacts strongly with SWNTs in dispersions and forms a donor-acceptor complex denoted NDI@SWNT. The interaction of this nanohybrid with cancer cells was explored using fluorescence microscopies. Chapter three describes the synthesis of series of molecular imaging agents based on two cancer targeting peptides (bombesin and RGDfK). Two types of NDIpeptide conjugates (Iodine-tagged NDI-Bombesin and Tryptophan-NDI-RGDfK) were designed and synthesized through EDC-coupling method. New compounds synthesized were characterised by mass spectroscopy and also HPLC. Fluorescence lifetime imaging microcopy and confocal laser scanning microscopy were utilised for investigating cellular behaviors (stability, fluorescence intensity and localization) of these molecular imaging probes. Chapter four describes the synthesis of amphiphilic conjugated thiophenes (dodecathiophene, denoted as T12). In this system, the thiophene backbone structure was chosen as a biocompatible coating for carbon nanotubes as simple molecular mechanics modeling suggested that it would be perfectly fitted to the curvature of SWNTs. T12 showed very good capability for debundling of SWNTs and forming corresponding solution dispersions of T12@SWNTs describes the potential of T12@SWNTs as a stable fluorescent bioimaging nano-probe for tracking cancer cells. Chapter five describes the successful filling of SWNTs with Cu2+ by radiochemistry methods (using 'hot' 64Cu ions anchored onto NaOAc) and also by a 'cold' optimised procedure for excess Cu(OAc)2. Filling with other metal ions was also tested, for example KReO4 and Zr(OAc)4. The filling experiments with Zr(OAc)4 in solution did not prove successful at normal pH but results were promising when pH was adjusted to ca. 2 by adding H2SO4. Any significant leakage of metal ions from open SWNTs was avoided by a simultaneous encapsulation of C70 molecules at the ends of SWNTs. Functionalisation of SWNTs by the supramolecular wrapping the surface of SWNTs in aqueous media with a naturally occurring glucan (β-1,3-1,4-Dglucan, denoted here as β-D-glucan) was also explored. Several boronic acid fluorophores were successfully synthesized and tested for the labeling of β-D-glucan @SWNTs by molecular recognition between boronic acids and this polysaccharide. Their cellular translocation behaviour and fluorescence properties were investigated by confocal fluorescence imaging and fluorescence lifetime imaging. Both methods show that localisation in sub-cellular (MCF-7 cells) regions and that the glucan coating significantly enhances the cell membrane translocation of SWNTs. Chapter six reports an efficient and economical strategy of supramolecular complex formulation of thermally reduced graphene. Naphthalene diimide (NDI) was used to form a stable and energy transfer complex which showed efficient quenching and significant red-shift of fluorescence of NDI when adsorbed onto graphene surfaces. The effect of thermally reducing annealing procedure to convert graphene oxides in graphene-nanoflake like materials was investigated. A new hybrid material (denoted here as NDI@TRG) synthesized was characterised by transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetric analysis (TGA) and fluorescence microscopy in the dispersed phase Chapter seven contains full experimental details for the work described in this thesis. The Appendix contains details of the crystallographic data and supplementary information on cell imaging photos and fluorescence lifetime point decay data for SWNT nanocomposites.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
Foram desenvolvidos nanocompósitos de óxidos dopados com níquel metálico pelo processo Sol-Gel modificado pelo uso do PVA (Álcool Polivinílico) na função de matriz de crescimento dos nanocompósitos. Os precursores dos óxidos foram os nitratos de seus próprios metais. Foram sintetizados três tipos de nanocompósitos óxido de magnésio, óxido de alumínio e óxido de zinco. O trabalho envolveu quatro etapas principais: levantamento bibliográfico, desenvolvimento e caracterização dos nanocompósitos e uso dos nanocompósitos como catalisadores na síntese de nanotubos de carbono. O desenvolvimento dos nanocompósitos foi motivado pela necessidade de materiais com tamanho e estrutura controláveis para emprego como catalisadores pela indústria. Na síntese dos nanocompósitos foi usada uma relação de PVA/ Água de 1/12 que depois foi variada para avaliar a influência sobre a força de hidrólise, a relação entre metal da matriz e níquel metálico foi de 9:1, em porcentagem em massa. Também foi avaliada a influência do surfactante Dodecil Sulfato de sódio (SDS) e do hidróxido de amônio na síntese dos nanocompósitos. Os nanocompósitos sintetizados neste trabalho foram testados como catalisadores no crescimento de nanotubos de carbono pela técnica de High Vacuum Chemical Vapor Deposition (CVD). Os catalisadores utilizados tinham tamanho de cristalito aproximado de 11nm no caso de óxido de magnésio e de 5 nm no caso do óxido de alumínio, o níquel metálico formado nestes suportes estava bem disperso e com dimensões estimadas de 3nm. Nanotubos de carbono de uma camada e mais de uma camada foram obtidas somente quando o suporte do níquel metálico era o óxido de magnésio. Os nanotubos foram caracterizados por Raman e microscopia eletrônica de varredura.
Metallic Nickel and oxide nanocomposite have been developed by Sol-Gel process modified by the use of PVA (polyvinyl alcohol) as a matrix for the growth of the nanocomposites. The oxides precursors were nitrates from their own metal. Three types of oxides were synthetized, magnesium oxide, aluminum oxide and zinc oxide. This work is presented in four sections: literature survey, development and characterization of nanocomposites and the use of nanocomposites as catalysts in the synthesis of carbon nanotubes. The development of these nanocomposites was motivated by the need for materials with controllable size and structure for use as catalysts in industry. The synthesis of the nanocomposites used a ratio of PVA / water of 1/12 that was later varied to evaluate the influence of the force of hydrolysis, the relationship between the matrix oxide metal and metallic nickel was 9:1 in mass percentage. The influence of the surfactant sodium dodecyl sulfate (SDS) and the ammonium hydroxide was also evaluated in the nanocomposites synthesis. The nanocomposites synthesized in this work were tested as catalysts in the growth of carbon nanotubes by the technique of High Vacuum Chemical Vapor Deposition (CVD). The catalysts used had a crystallite size of approximately 11nm in the case of magnesium oxide and 5 nm in the case of aluminum oxide, metallic nickel formed on these supports was well dispersed with a size of 3nm. Single layer and multiple layer carbon nanotubes were obtained only when magnesium oxide was the nickel substrate. The nanotubes were characterized by Raman and scanning electron microscopy.

Carbon nanotubes (CNTs) have captured a great deal of attention worldwide since their discovery in 1991. CNTs are considered to be the stiffest and strongest material due to their perfect atomic arrangement and intrinsic strong in-plane sp[super]2--sp[super]2 covalent bonds between carbon atoms. In addition to mechanical properties, CNTs have also shown exceptional chemical, electrical and thermal properties. All these aspects make CNTs promising candidates in the development of novel multi-functional nanocomposites. Utilizing CNTs as fillers to develop advanced nanocomposites still remains a challenge, due to the lack of fundamental understanding of both material processing at the nanometer scale and the resultant material properties. In this work, a new model was developed to investigate the amount of control specific parameters have on the mechanical properties of CNT composites. The new theory can be used to guide the development of advanced composites using carbon nanotubes, as well as other nano-fibers, with any matrices (ceramic, metal, or polymer). Our study has shown that the varying effect based on changes in CNT dimensions and concentration fit the model predictions very well. Metallic CNT composites using both single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes (MWNT), have been developed through a novel electrochemical co-deposition process. Copper and nickel matrix composites were developed by using pulse-reverse electrochemical co-deposition. Uniaxial tensile test results showed that a more than 300% increase in strength compared to that of the pure metal had been achieved. For example, the ultimate tensile strength of Ni/CNTs composites reached as high as about 2GPa. These are best experimental results ever reported within this field.; The mechanical results are mainly attributed to the good interfacial bonding between the CNTs and the metal matrices and good dispersion of carbon nanotubes within the matrices. Experimental results have also shown that the strength is inversely dependent on the diameter of carbon nanotubes. In addition to the mechanical strength, carbon nanotube reinforced metallic composites are excellent multifunctional materials in terms of electrical and thermal conduction. The electrical resistivity of carbon nanotube/copper composites produces electrical resistivity of about 1.0~1.2 x10[super]-6ohm-cm, which is about 40% less than the pure copper. The reduced electrical resistivity is also attributed to the good interfacial bonding between carbon nanotubes and metal matrices, realized by the electrochemical co-deposition.
ID: 028916756; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 95-105).
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science

Ce travail de thèse est d’utilisation de nanotubes de carbon (NTCs) comme support pour confiner de nanoparticules métalliques ou comme gabarit pour le confinement de la phase active. Le chapitre I présente l’état actuel des connaissances sur les effets de confinement dans les NTCs. Le chapitre II décrit la préparation et la caractérisation de catalyseurs métalliques à base de ruthénium, de cobalt et de palladium, confinées à l’intérieur de NTCs. Dans ce cadre, l’étude de l’influence de différents paramètres tels que les conditions opératoires, la nature du métal ou du précurseur, ou un prétraitement du support NTC, sur la sélectivité du confinement est présentée. Le chapitre III comporte deux parties : l’une est consacrée à l’utilisation de NTCs comme gabarit pour la synthèse de nanotubes de silice (NTSs, en présence ou non de particules de ruthénium confinées dans leur canal). L’autre partie concerne l’immobilisation du catalyseur (complexe métallique de rhodium) dans une phase liquide ionique comme phase catalytique active avant le remplissage dans les NTCs. Le chapitre IV concerne l’application tous les systèmes catalytiques à base de catalyseurs confinés à l’intérieur de nanotubes dans les réactions d’hydrogénation du cinnamaldéhyde et du 1-hexène. L’effet de confinement sur les performances catalytiques est présenté
This thesis is refer of carbon nanotubes (CNTs) as a support to confine metal nanoparticles or as a template for the confinement of the active phase. Chapter I give a comprehensive review of the state of knowledge on the effects of confinement in CNTs. Chapter II describes the preparation and characterization of the metals (ruthenium, palladium and cobalt) confined inside CNTs catalysts. In this context, the study of the influence of various parameters such as operating conditions, nature of the metal or precursor or nanosupport pretreatment, on the selectivity of confinement is presented. Chapter III consists of two parts: one is devoted to the using of CNTs as a template for the synthesis of silica nanotubes (SNTs in the presence or absence of ruthenium particles confined in their channel). The other part is the immobilization of the catalyst (rhodium metallic complex) in an ionic liquid phase as active catalytic phase before filling in CNTs. Chapter IV concernes the application all catalyst-filled CNTs systems in the hydrogenation of cinnamaldehyde and 1-hexene reaction. The confinement effect on the catalytic performance is presented

Le diamant est un matériau fascinant avec d'exceptionnelles propriétés physiques. Son application à divers domaines reste limitée parce que sa fabrication est difficile et nécessite des substrats et conditions spécifiques. En outre, les dispositifs de diamant tels que les capteurs nécessitent généralement la structuration et l'échelle micro ou nanométrique, et l'inertie chimique du diamant rend ce processus technologique plus difficile que celui des semiconducteurs réguliers. Il s'agit d'un besoin évident de la recherche fondamentale d’explorer de nouvelles façons de fabriquer des nanostructures de diamant, ce qui permet de nouvelles formes de capteurs et dispositifs. Dans ce contexte, le travail présenté est d'une grande importance pour la communauté de diamant et pour le développement futur de la technologie du diamant.Le manuscrit est divisé en huit parties: une introduction; 6 chapitres, une conclusion générale. Dans l'introduction le contexte de l'étude est brièvement présenté avec les deux objectifs. Le premier consistait à étudier la croissance des nanofils de diamant et à trouver des conditions appropriées pour obtenir des nanofils de façon reproductible. Le deuxième objectif était la mise au point du procédé de gravure du diamant avec des particules de catalyseur et de l'optimisation des paramètres du procédé.Le premier chapitre de ce manuscrit présente tout d'abord l'état de l’art en mat ière de propriétés et des technologies de croissance du diamant. Puis, dans le deuxième chapitre, en vue de la croissance des nanofils et des études de gravure de nanostructures utilisées catalyseurs métalliques, la base de l'interaction métal-carbone est présenté.Le chapitre trois contient l'instrumentation et principe de fonctionnement des techniques expérimentales et analytiques utilisées dans cette étude. Le chapitre suivant se concentre sur la recherche de conditions favorables à la croissance des nanofils de diamant, d'abord en étudiant en détail un processus signalé en 2005 qui a conduit à la nucléation des nanocristaux sur des nanotubes de carbone, puis la croissance de nanofils.Les conditions de croissance ont été soigneusement reproduites, sans succès reproductible. Il en est déduit déduit que d'un élément non a contribué à la croissance, comme une contamination du catalyseur. La combinaison avec le fait que le processus publiée en 2005 n'a jamais été reproduite, en dépit de son importance technologique élevé, ce qui suggère que la contamination s'est produite également dans cette oeuvre originale.Puis, à partir de cette première observation, l'effet d'un catalyseur a été étudié, et des résultats intéressants ont été obtenus. Les nanofils ont été obtenus de façon reproductible, mais le point important est que les nanofils à base de silicium sont très faciles à cultiver, et qu'un environnement deCarbone pur était nécessaire d'étudier la croissance de nanofils de carbone. Dans ces conditions, un continuum allant de diamant de gravure pour la croissance du diamant a été obtenue en fonction de l'apport de carbone, très intéressant pour la technologie du diamant. Dans le cinquième chapitre du mécanisme de gravure de diamant par des particules de catalyseur est explorée. La gravure à motifs a été proposée pour la fabrication de nano-ou micro-structures dans le diamant, et il est présenté dans la dernière partie de ce chapitre. Le chapitre 6 présente deux applications intéressantes du processus dedéveloppement. Les premières membranes poreuses préoccupations utilisés comme bio-capteurs, et les nanotubes de carbone second concerne la base neuro-capteurs.Malgré l'étude infructueuse de la croissance du diamant nanofil, le travail fait des progrès significatifs à la science de la croissance matérielle nanocarbone. Et elle a conduit à l'étude approfondie de gravure diamant, qui est également très important pour la technologie
One-dimensional structures with nanometre diameters, such as nanotubes and nanowires, have attracted extensive interest in recent years and form new family of materials that have characteristic of low weight with sometimes exceptional mechanical, electrical and thermal properties. Without any change in chemical composition, fundamental properties of bulk materials can be enhanced at the nanometre scale leading to extraordinary nanodevices.Since a few years, nanowires of different semiconducting materials have been grown. To mention few of these, Si, GaN, SnO, SiC and ZnO nanowires were all successfully demonstrated. However, the growth of diamond nanowires has not yet been demonstrated, despite the strong interest for this material. Bulk diamond combines various exceptional properties for a wide range of applications: Chemical inertness, radiation hardness, biocompatibility, high hole/electron mobility (2000/1000 cm2/V/s), high thermal conductivity (22 W/cm/K), wide bandgap (5.5 eV), and wide electric potential window (3.25 eV H-O evolutions).Since about 30 years, the growth of diamond thin film is well controlled either as insulator or as semiconductor with p- and n- type dopants. Fabrication of 25x25 mm2 monocrystalline diamond wafer has already been reported, and two inches wafers are expected in a couple of years demonstrating the growing interest for this material. Among present or short-term applications one can mention alpha-particle detectors, solar-blind UV sensors, high voltage electronic devices, bio-sensors and single photon source. The realization of nanowires should improve the performance of some of these devices and also open a range of new high performance applications.The stability of 0D (nanocrystals) and 1D (nanowires) diamond nanostructures has been extensively studied using ab initio modelling and indicates that for specific crystallographic orientations clusters of nanometric size are thermodynamically stable. One experimental indication for diamond nanowire growth has been published by Sun et al. in 2005, based on nanocrystal nucleation and growth on carbon nanotubes followed by 1D growth. This particular nucleation process on carbon nanotube has furthermore been explained theoretically in 2009.Based on these experimental and theoretical results, the first objective of this thesis was to explore the growth of diamond nanowire and find suitable conditions to obtain nanowires in a reproducible way. A wide range of process conditions were explored, first without any catalyst, then with metallic catalyst in order to promote Vapour-Liquid-Solid (VLS) growth. Although a comprehensive knowledge regarding carbon nanotube stability in hydrogen atmosphere and diamond-catalyst interaction has been obtained and some carbon nanostuctures were grown, no diamond nanowires were obtained in a reproducible way.However, the careful study of the diamond-catalyst interaction revealed a very interesting etching process that could be very useful for the fabrication of diamond nanostructures. A second objective was then defined: development of the etching process for diamond using transition metal as catalyst and optimization of the process parameters for specific applications such as the fabrication of porous diamond membranes for bio-sensors

The current-voltage characteristics of a triode with the plane-parallel electrodes and a cold cathode based on the ordered array of single-wall metallic carbon nanotubes with open ends have been calculated by means of a numerical solution of both the Poisson equation and the quantum-wave equation. The topological parameters of the triode have been optimized. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35361

Les nanomatériaux carbonés tels que les nanotubes de carbone (CNTs) et le graphène, suscitent un engouement certain dans toute la communauté scientifique depuis leur découverte. En effet, leur taille nanométrique et leur structure unique leur confèrent de nombreuses propriétés jusqu'alors inégalées par les matériaux connus. Grâce à leur nature « tout-carbone », ils sont stables chimiquement, possèdent une bonne tenue mécanique et une surface spécifique élevée. Cependant les échantillons produits et disponibles pour développer des applications contiennent inévitablement des impuretés (de nature métallique et carbonée). Ces dernières gênent considérablement l’exploitation des propriétés des CNTs et le transfert technologique vers les applications potentielles. Un traitement de purification post-synthèse de ces nanoparticules s’avère donc indispensable. Des méthodes de purification existent mais ne sont pas satisfaisantes puisqu’elles sont multi-étapes, chronophages, complexes et à faible rendement. Ce travail de thèse avait pour objectif de développer une méthode alternative de purification des CNTs. L’utilisation d’un couplage de gaz réactionnels (le dichlore et le dioxygène) a permis de proposer une approche originale qui requiert un seul traitement et qui permet d’augmenter substantiellement la sélectivité d’élimination des impuretés tout en préservant les CNTs. Les rendements obtenus par cette méthode sont donc élevés. En plus de sa simplicité et de son efficacité, ce traitement a l’énorme avantage de convenir à plusieurs types d’échantillons de CNTs. Enfin, ces travaux ont un fort impact en termes socio-économique et d’innovation puisque ces nanoparticules sont au service du développement durable. Les échantillons de CNTs purifiés obtenus ont notamment été testés pour la production de nanofluides pour des applications de transfert thermique dans les panneaux solaires. Nous avons également montré que ces nanomatériaux, une fois fonctionnalisés, présentaient un intérêt certain dans les procédés de synthèse verts, notamment en bio-catalyse enzymatique
Since their discovery, carbon nanomaterials such as carbon nanotubes (CNTs) and graphene have raised a great interest in the scientific community. Indeed, they are impressive materials thanks to their unique and remarkable properties: nanometric size and lightness, high chemical stability due to their all-carbon structure, high specific surface area. However, after their synthesis, available CNT samples contain impurities (metallic catalyst residues and carbonaceous). These unwanted particles hinder exploitation of the properties of the CNTs and thus prevent the scale-up transfer. This is the reason why a post-synthesis purification treatment is required. Existing standard methods are often too aggressive, time-consuming because of the multi steps involved and they lead to low sample yields. In this work, we have developed an alternative purification approach. The combination of two reactants in gas phase (chlorine and dioxygen) allowed us to propose an original method consisting of a one-pot treatment. Thanks to this simple technique, we were able to substantially enhance the removal selectivity of both metallic based and carbonaceous impurities while preserving CNT quality; the sample yields obtained with our method are indeed high. In addition to its simplicity and efficiency, this method is versatile since it has been successfully applied to various types of CNTs. Finally, these works have a significant social-economic impact and in terms of innovation because these purified CNTs can be used for sustainable development. The prepared CNT-based nanofluids have the potential to be utilized as heat transfer fluid in solar panels. We have also shown that these carbon nanomaterials, once being functionalized, had a high interest in green synthesis methods, in particular in enzymatic biocatalysis

Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) are attractive reinforcements for lightweight and high strength metal matrix composites due to their excellent mechanical and physical properties. The present work is an attempt towards investigating the effect of CNT and GNP reinforcements on the mechanical properties of nickel matrix composites. The CNT/Ni (dry milled) nanocomposites exhibiting a tensile yield strength of 350 MPa (about two times that of SPS processed monolithic nickel ~ 160 MPa) and an elongation to failure ~ 30%. In contrast, CNT/Ni (molecular level mixed) exhibited substantially higher tensile yield strength (~ 690 MPa) but limited ductility with an elongation to failure ~ 8%. The Ni-1vol%GNP (dry milled) nanocomposite exhibited the best balance of properties in terms of strength and ductility. The enhancement in the tensile strength (i.e. 370 MPa) and substantial ductility (~40%) of Ni-1vol%GNP nanocomposites was achieved due to the combined effects of grain refinement, homogeneous dispersion of GNPs in the nickel matrix, and well-bonded Ni-GNP interface, which effectively transfers stress across metal-GNP interface during tensile deformation. A second emphasis of this work was on the detailed 3D microstructural characterization of a new class of Ni-Ti-C based metal matrix composites, developed using the laser engineered net shaping (LENSTM) process. These composites consist of an in situ formed and homogeneously distributed titanium carbide (TiC) as well as graphite phase reinforcing the nickel matrix. 3D microstructure helps in determining true morphology and spatial distribution of TiC and graphite phase as well as the phase evolution sequence. These Ni-TiC-C composites exhibit excellent tribological properties (low COF), while maintaining a relatively high hardness.

Les nanomatériaux carbonés (NMC) sont très utilisés dans le monde industriel et leurs applications, nombreuses, sont en plein développement. L’absence de réglementation pour leur préparation et leur emploi fait qu’il est nécessaire comme pour tous les nano-objets, de déterminer le risque qu’une exposition fait courir à l’Homme et d’adapter la législation en conséquence. Une meilleure connaissance de leur potentiel toxique est donc nécessaire. Les difficultés de plus en plus grandes pour utiliser les modèles animaux, rend nécessaire le développement d’études avec des lignées cellulaires au sein desquelles les macrophages ont une place prépondérante. Ces NMC sont très légers et forment facilement des aérosols et les modèles préférés sont les macrophages alvéolaires. Cependant il n’existe pas à l’heure actuelle de lignées de macrophages alvéolaires humains à la différence de cellules de rat. Le sujet de ma thèse porte sur l’étude de la réponse macrophagique aux NMC et la compréhension des effets de leurs caractéristiques physiques et chimiques sur leur transcriptome. Les NMC étudiés sont les nanotubes de carbone (NTC) multi feuillets, les NTC mono feuillets, le noir de carbone et l’oxyde de graphène. Nos résultats montrent que tous les NMC étudiés déclenchent une réaction inflammatoire dans les cellules NR8383 et les cellules THP-1 différenciées, et certains d’entre eux induisent une cytotoxicité importante. La taille, la fonctionnalisation et la forme contrôlent les mécanismes de toxicité induits par les NMC. Des NTC de tailles similaires altèrent des voies de signalisation identiques, une fonctionnalisation par des groupements amines produit un stress des lysosomes tandis que la fonctionnalisation par des groupements carboxyle entraine un stress du réticulum endoplasmique (RE). Les nanotubes induisent une désorganisation du cytosquelette plus importante que les nanoparticules sphériques. Nous avons également mis en évidence une accumulation de lipides chez les cellules NR8383 suite à un stress du RE induit par le Mitsui-7, un NTC multi feuillet. Le même NTC induit aussi une fusion de ces macrophages. La formation de ces cellules spumeuses et des cellules géantes à multi-noyaux sont des évènements clés entrainant la formation de granulomes. Les résultats obtenus présentent un support important pour la compréhension des effets des NMC montrant une certaine toxicité non négligeable de point de vue moléculaire. Cette toxicité est dépendante des caractéristiques physiques et chimiques de ces nanomatériaux. Ainsi, en se basant sur ce type de données, on pourra s’orienter vers une fabrication safe-by-design pour limiter les risques liés à leur exposition
Carbon nanomaterials (CNM) are widely used in the industrial world and they have many applications. The absence of legislation controlling their preparation and uses makes necessary, as for all nano-objects, the study of their toxicity in order to determine the risk of human exposure and to adapt legislation accordingly. Therefore, a better knowledge of their toxic potential is necessary. The increasing difficulties in using animal models make necessary the development of studies using cell lines especially macrophages that play a predominant role. These CNM are very light and form easily aerosols, reason why the preferred models for toxicity studies are alveolar macrophages. However, there are no human alveolar macrophage lines currently but rat cells exist. The subject of my thesis is to study macrophages response to CNM and the understanding of the effect of their physical and chemical characteristics on the transcriptome. The CNM studied are multiwall carbon nanotubes (CNT), single wall CNT, carbon black and graphene oxide. Our results show that all CNM studied trigger an inflammatory reaction in NR8383 and differentiated THP-1 cells, also some of them induce cytotoxicity. Size, functionalization and form control CNM toxicity mechanisms: CNT with similar size alter identical signaling pathways, amino group functionalization produces lysosomal stress, whereas functionalization with carboxyl groups causes reticulum endoplasmic (RE) stress, nanotubes induce cytoskeleton disorganization more than spherical nanoparticles. Otherwise, we identified lipid accumulation in NR8383 cells due to RE stress induced by Mitsui-7, a multiwall CNT. There was also a fusion of these macrophages. The formation of these foam cells and giant multi-nucleus cells are key events leading to granulomas formation. The results obtained are an important support for understanding CNM effects, showing some significant toxicity at molecular level. This toxicity is dependent on the physical and chemical characteristics of these nanomaterials. Thus, based on this type of data, we can move towards a safer manufacture to avoid the risks associated with their exposure

(ULSI) causes an increase of the resistance of the wiring system by increased scattering of electrons at side walls and grain boundaries in the state of the art Cu technology, which increases the RC delay of the interconnect system and thus degrades the performance of the device. The outstanding properties of carbon nanotubes (CNT) such as a large mean free path, a high thermal conductance and a large resistance against electromigration make them an ideal candidate to replace Cu in future feature nodes. The present thesis contributes to the preparation and properties of CNT based vertical interconnections (vias). In addition, all processes applied during the fabrication are compatible to ULSI and an interface between CNT based vias and a Cu metallization is studied. The methodology for the evaluation of CNT based vias is improved; it is highlighted that by measuring the resistance of one multiwall CNT and taking into account the CNT density, the performance of the CNT based vias can be predicted accurately. This provides the means for a systematic evaluation of different integration procedures and materials. The lowest contact resistance is obtained for carbide forming metals, as long as oxidation during the integration is avoided. Even though metal-nitrides exhibit an enhanced contact resistance, they are recommended to be used at the bottom metallization in order to minimize the oxidation of the metal-CNT contact during subsequent processing steps. Overall a ranking for the materials from the lowest to the highest contact resistance is obtained: Ta < Ti < TaN < TiN « TiO2 « Ta2O5 Furthermore the impact of post CNT growth procedures as chemical mechanical planarization, HF treatment and annealing procedures after the CNT based via fabrication are evaluated. The conductance of the incorporated CNTs and the applicable electrical transport regime relative to the CNT quality and the CNT length is discussed. In addition, a strong correlation between the temperature coefficient of resistance and the initial resistance of the CNT based vias at room temperature has been observed.
Die kontinuierliche Miniaturisierung der charakteristischen Abmessungen in hochintegrierten Schaltungen (ULSI) verursacht einen Anstieg des Widerstandes im Zuleitungssystem aufgrund der erhöhten Streuung von Elektronen an Seitenwänden und Korngrenzen in der Cu-Technologie, wodurch die Verzögerungszeit des Zuleitungssystems ansteigt. Die herausragenden Eigenschaften von Kohlenstoffnanoröhren (CNT), wie eine große mittlere freie Weglänge, hohe thermische Leitfähigkeit und eine starke Resistenz gegenüber Elektromigration machen diese zu einem idealen Kandidaten, um Cu in zukünftigen Technologiegenerationen zu ersetzen. Die vorliegende Arbeit beschreibt die Herstellung und daraus resultierenden Eigenschaften von Zwischenebenenkontakten (Vias) basierend auf CNTs. Alle verwendeten Prozessierungsschritte sind kompatibel mit der Herstellung von hochintegrierten Schaltkreisen und eine Schnittstelle zwischen den CNT Vias und einer Cu-Metallisierung ist vorhanden. Insbesondere das Verfahren zur Evaluierung von CNT Vias wurde durch den Einsatz verschiedener Methoden verbessert. Insbesondere soll hervorgehoben werden, dass durch die Messung des Widerstandes eines einzelnen CNTs, bei bekannter CNT Dichte, der Via Widerstand sehr genau vorausgesagt werden kann. Dies ermöglicht eine systematische Untersuchung des Einflusses der verschiedenen Prozessschritte und der darin verwendeten Materialien auf den Via Widerstand. Der niedrigste Kontaktwiderstand wird für Karbidformierende Metalle erreicht, solange Oxidationsprozesse ausgeschlossen werden können. Obwohl Metallnitride einen höheren Kontaktwiderstand aufweisen, sind diese für die Unterseitenmetallisierung zu empfehlen, da dadurch die Oxidation der leitfähigen Schicht minimiert wird. Insgesamt kann eine Reihenfolge beginnend mit dem niedrigsten zum höchsten Kontaktwiderstand aufgestellt werden: Ta < Ti < TaN < TiN « TiO2 « Ta2O5 Desweiteren wurde der Einfluss von Verfahren nach dem CNTWachstum wie die chemischmechanische Planarisierung, eine HF Behandlung und einer Temperaturbehandlung evaluiert, sowie deren Einfluss auf die elektrischen Parameter des Vias untersucht. Die Leitfähigkeit der integrierten CNTs und die daraus resultierenden elektrischen Transporteigenschaften in Abhängigkeit der CNT Qualität und Länge werden besprochen. Ebenso wird die starke Korrelation zwischen dem Temperaturkoeffizienten des elektrischen Widerstandes und des Ausgangswiderstandes der CNT basierten Vias bei Raumtemperatur diskutiert.

(ULSI) causes an increase of the resistance of the wiring system by increased scattering of electrons at side walls and grain boundaries in the state of the art Cu technology, which increases the RC delay of the interconnect system and thus degrades the performance of the device. The outstanding properties of carbon nanotubes (CNT) such as a large mean free path, a high thermal conductance and a large resistance against electromigration make them an ideal candidate to replace Cu in future feature nodes. The present thesis contributes to the preparation and properties of CNT based vertical interconnections (vias). In addition, all processes applied during the fabrication are compatible to ULSI and an interface between CNT based vias and a Cu metallization is studied. The methodology for the evaluation of CNT based vias is improved; it is highlighted that by measuring the resistance of one multiwall CNT and taking into account the CNT density, the performance of the CNT based vias can be predicted accurately. This provides the means for a systematic evaluation of different integration procedures and materials. The lowest contact resistance is obtained for carbide forming metals, as long as oxidation during the integration is avoided. Even though metal-nitrides exhibit an enhanced contact resistance, they are recommended to be used at the bottom metallization in order to minimize the oxidation of the metal-CNT contact during subsequent processing steps. Overall a ranking for the materials from the lowest to the highest contact resistance is obtained: Ta < Ti < TaN < TiN « TiO2 « Ta2O5 Furthermore the impact of post CNT growth procedures as chemical mechanical planarization, HF treatment and annealing procedures after the CNT based via fabrication are evaluated. The conductance of the incorporated CNTs and the applicable electrical transport regime relative to the CNT quality and the CNT length is discussed. In addition, a strong correlation between the temperature coefficient of resistance and the initial resistance of the CNT based vias at room temperature has been observed
Die kontinuierliche Miniaturisierung der charakteristischen Abmessungen in hochintegrierten Schaltungen (ULSI) verursacht einen Anstieg des Widerstandes im Zuleitungssystem aufgrund der erhöhten Streuung von Elektronen an Seitenwänden und Korngrenzen in der Cu-Technologie, wodurch die Verzögerungszeit des Zuleitungssystems ansteigt. Die herausragenden Eigenschaften von Kohlenstoffnanoröhren (CNT), wie eine große mittlere freie Weglänge, hohe thermische Leitfähigkeit und eine starke Resistenz gegenüber Elektromigration machen diese zu einem idealen Kandidaten, um Cu in zukünftigen Technologiegenerationen zu ersetzen. Die vorliegende Arbeit beschreibt die Herstellung und daraus resultierenden Eigenschaften von Zwischenebenenkontakten (Vias) basierend auf CNTs. Alle verwendeten Prozessierungsschritte sind kompatibel mit der Herstellung von hochintegrierten Schaltkreisen und eine Schnittstelle zwischen den CNT Vias und einer Cu-Metallisierung ist vorhanden. Insbesondere das Verfahren zur Evaluierung von CNT Vias wurde durch den Einsatz verschiedener Methoden verbessert. Insbesondere soll hervorgehoben werden, dass durch die Messung des Widerstandes eines einzelnen CNTs, bei bekannter CNT Dichte, der Via Widerstand sehr genau vorausgesagt werden kann. Dies ermöglicht eine systematische Untersuchung des Einflusses der verschiedenen Prozessschritte und der darin verwendeten Materialien auf den Via Widerstand. Der niedrigste Kontaktwiderstand wird für Karbidformierende Metalle erreicht, solange Oxidationsprozesse ausgeschlossen werden können. Obwohl Metallnitride einen höheren Kontaktwiderstand aufweisen, sind diese für die Unterseitenmetallisierung zu empfehlen, da dadurch die Oxidation der leitfähigen Schicht minimiert wird. Insgesamt kann eine Reihenfolge beginnend mit dem niedrigsten zum höchsten Kontaktwiderstand aufgestellt werden: Ta < Ti < TaN < TiN « TiO2 « Ta2O5 Desweiteren wurde der Einfluss von Verfahren nach dem CNTWachstum wie die chemischmechanische Planarisierung, eine HF Behandlung und einer Temperaturbehandlung evaluiert, sowie deren Einfluss auf die elektrischen Parameter des Vias untersucht. Die Leitfähigkeit der integrierten CNTs und die daraus resultierenden elektrischen Transporteigenschaften in Abhängigkeit der CNT Qualität und Länge werden besprochen. Ebenso wird die starke Korrelation zwischen dem Temperaturkoeffizienten des elektrischen Widerstandes und des Ausgangswiderstandes der CNT basierten Vias bei Raumtemperatur diskutiert

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

Vor dem Hintergrund zukünftiger Sensoren, basierend auf dem piezoresistiven Effekt von einwandigen Kohlenstoffnanoröhren (SWCNT), werden in dieser Arbeit umfangreiche Ergebnisse zum mechanischen Verhalten von Grenzflächen zwischen SWCNTs und edlen Metallen am Beispiel von Pd und Au präsentiert. Im Fokus steht dabei die Synergie von rechnerischen und experimentellen Methoden Molekulardynamik (MD), nanoskalige Tests und Analytik , um (1) mit guter Genauigkeit maximale Kräfte von gezogenen SWCNTs, welche in Metall eingebettet sind, vorauszuberechnen und (2) einen wertvollen Beitrag zum Verständnis der zu Grunde liegenden Fehlermechanismen zu liefern. Es wurde ein MDModell eines in eine einkristalline Matrix eingebetteten SWCNTs mit Randbedingen eines Auszugsversuchs entwickelt. Mit diesem Modell können Kraft-Weg-Beziehungen und Energieverläufe für einen quasistatischen verschiebungsgesteuerten Auszugsversuch errechnet werden. Das Modell liefert kritische Kräfte bei Versagen des Systems. Des Weiteren können mit diesem Modell der Einfluss des SWCNT-Typus, der Einbettungslänge, der Temperatur, von intrinsischen Defekten und Oberflächengruppen (SFGs) auf das Grenzflächenverhalten untersucht werden. Zum Vergleich wurden kritische Kräfte experimentell durch in situ Auszugsversuche in einem Rasterelektronenmikroskop bestimmt. Es wurde eine sehr gute Übereinstimmung von rechnerischen und experimentellen Daten festgestellt. Der vorherrschende Fehler im Experiment ist der SWCNT-Bruch, jedoch wurden auch einige SWCNT-Auszüge beobachtet. Mit Hilfe der MD-Simulationen wurde gefunden, dass die SFGs als kleine Anker in der umgebenden metallischen Matrix wirken und somit die maximalen Kräfte signifikant erhöhen. Diese Grenzflächenverstärkung kann Zugspannungen verursachen, die genügend hoch sind, so dass SWCNT-Bruch initiert wird. Im Gegensatz dazu zeigten Simulationen von Auszugstests mit idealen SWCNTs nur kleine Auszugskräfte, welche meistens unabhängig von der Einbettungslänge des SWCNTs sind. Dieses Verhalten wird mit einer inkommensurablen Konfiguration der Kristallstrukturen an der Grenzfläche von SWCNTs und der einbettenden Edelmetalle interpretiert. Zur Qualifizierung der Existenz von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material wurden analytische Untersuchungen mittels Fluoreszenzmarkierung von Oberflächengruppen durchgeführt. In Übereinstimmung mit Literaturstellen zum gesicherten Nachweis von SFGs, bedingt durch technologische Behandlungen, weisen diese Experimente stark auf das Vorhandensein von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material hin. Demnach kann der dominante SWCNT-Bruch Fehler durch die Grenzflächenverstärkung auf Grund von SFGs erklärt werden
In the light of future sensors, that are based upon the piezoresistive effect of singlewalled carbon nanotubes (SWCNTs), this work presents comprehensive results of studies on the mechanical behavior of interfaces between SWCNTs and noble metals using the examples of Pd and Au. With this contribution, the focus is on a synergy between computational and experimental approaches involving molecular dynamics (MD) simulations, nanoscale testing, and analytics (1) to predict to a good degree of accuracy maximum forces of pulled SWCNTs embedded in a noble metal matrix and (2) to provide valuable input to understand the underlying mechanisms of failure. A MD model of a SWCNT embedded in a single crystalline matrix with pull-out test boundary conditions was developed. With this model, force-displacement relations and energy evolutions for a quasi-static displacement controlled test can be computed. The model provides critical forces for failure of the system. Furthermore, the influence of SWCNT type, embedding length, temperature, intrinsic defects and surface functional groups (SFGs) on the interface behavior can be studied using this model. For comparison, critical forces were experimentally determined by conducting pull-out tests in situ, inside a scanning electron microscope. A very good agreement of computational and experimental values was discovered. The dominant failure mode in the experiment was a SWCNT rupture, although several pull-out failures were also observed. From MD simulations, it was found that SFGs act as small anchors in the metal matrix and significantly enhance the maximum forces. This interface reinforcement can lead to tensile stresses sufficiently high to initiate SWCNT rupture. In contrast, pull-out test simulations of ideal SWCNTs show only small pull-out forces, which are mostly independent on SWCNT embedding length. This behavior is interpreted with an incommensurate configuration of crystal structures at the interface between SWCNTs and embedding noble metals. To qualify the existence of carboxylic SFGs on the used SWCNT material, an analytical investigation by means of fluorescence labeling of surface species was performed. In agreement with literature reports on the secured verification of SFGs due to necessary technological treatments, these experiments strongly indicate the presence of carboxylic SFGs on the used SWCNT material. Thus, the dominant SWCNT rupture failure is explained with an interface reinforcement by SFGs

Vor dem Hintergrund zukünftiger Sensoren, basierend auf dem piezoresistiven Effekt von einwandigen Kohlenstoffnanoröhren (SWCNT), werden in dieser Arbeit umfangreiche Ergebnisse zum mechanischen Verhalten von Grenzflächen zwischen SWCNTs und edlen Metallen am Beispiel von Pd und Au präsentiert. Im Fokus steht dabei die Synergie von rechnerischen und experimentellen Methoden Molekulardynamik (MD), nanoskalige Tests und Analytik , um (1) mit guter Genauigkeit maximale Kräfte von gezogenen SWCNTs, welche in Metall eingebettet sind, vorauszuberechnen und (2) einen wertvollen Beitrag zum Verständnis der zu Grunde liegenden Fehlermechanismen zu liefern. Es wurde ein MDModell eines in eine einkristalline Matrix eingebetteten SWCNTs mit Randbedingen eines Auszugsversuchs entwickelt. Mit diesem Modell können Kraft-Weg-Beziehungen und Energieverläufe für einen quasistatischen verschiebungsgesteuerten Auszugsversuch errechnet werden. Das Modell liefert kritische Kräfte bei Versagen des Systems. Des Weiteren können mit diesem Modell der Einfluss des SWCNT-Typus, der Einbettungslänge, der Temperatur, von intrinsischen Defekten und Oberflächengruppen (SFGs) auf das Grenzflächenverhalten untersucht werden. Zum Vergleich wurden kritische Kräfte experimentell durch in situ Auszugsversuche in einem Rasterelektronenmikroskop bestimmt. Es wurde eine sehr gute Übereinstimmung von rechnerischen und experimentellen Daten festgestellt. Der vorherrschende Fehler im Experiment ist der SWCNT-Bruch, jedoch wurden auch einige SWCNT-Auszüge beobachtet. Mit Hilfe der MD-Simulationen wurde gefunden, dass die SFGs als kleine Anker in der umgebenden metallischen Matrix wirken und somit die maximalen Kräfte signifikant erhöhen. Diese Grenzflächenverstärkung kann Zugspannungen verursachen, die genügend hoch sind, so dass SWCNT-Bruch initiert wird. Im Gegensatz dazu zeigten Simulationen von Auszugstests mit idealen SWCNTs nur kleine Auszugskräfte, welche meistens unabhängig von der Einbettungslänge des SWCNTs sind. Dieses Verhalten wird mit einer inkommensurablen Konfiguration der Kristallstrukturen an der Grenzfläche von SWCNTs und der einbettenden Edelmetalle interpretiert. Zur Qualifizierung der Existenz von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material wurden analytische Untersuchungen mittels Fluoreszenzmarkierung von Oberflächengruppen durchgeführt. In Übereinstimmung mit Literaturstellen zum gesicherten Nachweis von SFGs, bedingt durch technologische Behandlungen, weisen diese Experimente stark auf das Vorhandensein von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material hin. Demnach kann der dominante SWCNT-Bruch Fehler durch die Grenzflächenverstärkung auf Grund von SFGs erklärt werden.
In the light of future sensors, that are based upon the piezoresistive effect of singlewalled carbon nanotubes (SWCNTs), this work presents comprehensive results of studies on the mechanical behavior of interfaces between SWCNTs and noble metals using the examples of Pd and Au. With this contribution, the focus is on a synergy between computational and experimental approaches involving molecular dynamics (MD) simulations, nanoscale testing, and analytics (1) to predict to a good degree of accuracy maximum forces of pulled SWCNTs embedded in a noble metal matrix and (2) to provide valuable input to understand the underlying mechanisms of failure. A MD model of a SWCNT embedded in a single crystalline matrix with pull-out test boundary conditions was developed. With this model, force-displacement relations and energy evolutions for a quasi-static displacement controlled test can be computed. The model provides critical forces for failure of the system. Furthermore, the influence of SWCNT type, embedding length, temperature, intrinsic defects and surface functional groups (SFGs) on the interface behavior can be studied using this model. For comparison, critical forces were experimentally determined by conducting pull-out tests in situ, inside a scanning electron microscope. A very good agreement of computational and experimental values was discovered. The dominant failure mode in the experiment was a SWCNT rupture, although several pull-out failures were also observed. From MD simulations, it was found that SFGs act as small anchors in the metal matrix and significantly enhance the maximum forces. This interface reinforcement can lead to tensile stresses sufficiently high to initiate SWCNT rupture. In contrast, pull-out test simulations of ideal SWCNTs show only small pull-out forces, which are mostly independent on SWCNT embedding length. This behavior is interpreted with an incommensurate configuration of crystal structures at the interface between SWCNTs and embedding noble metals. To qualify the existence of carboxylic SFGs on the used SWCNT material, an analytical investigation by means of fluorescence labeling of surface species was performed. In agreement with literature reports on the secured verification of SFGs due to necessary technological treatments, these experiments strongly indicate the presence of carboxylic SFGs on the used SWCNT material. Thus, the dominant SWCNT rupture failure is explained with an interface reinforcement by SFGs.

Through polarization-dependent magneto-optical absorption spectroscopy, the magnetic susceptibility anisotropy for metallic single-walled carbon nanotubes has been extracted and found to be up to 4x greater than values for semiconducting single-walled carbon nanotubes. Consistent with theoretical predictions, this is the first experimental evidence of the paramagnetic nature arising from the Aharonov-Bohm-phase-induced gap opening in metallic nanotubes. We also compare our values with previous work for semiconducting nanotubes, which confirm a break from the prediction that the magnetic susceptibility anisotropy increases linearly with the diameter.

The continuous migration to smaller feature sizes puts high demands on materials and technologies for future ultra-large-scale integrated circuits. Particularly, the copper-based interconnect system will reach fundamental limits soon. Their outstanding properties make metallic carbon nanotubes (CNTs) an ideal material to partially replace copper in future interconnect architectures. Here, a low contact resistance to existing metal lines is crucial. The present thesis contributes to the theory and numerical description of electronic transport in metallic CNTs with metal contacts. Different theoretical approaches are applied to various contact models and electrode materials (Al, Cu, Pd, Ag, Pt, Au) are compared. Ballistic transport calculations are based on the non-equilibrium Greens function formalism combined with tight-binding (TB), extended Hückel theory (EHT) and density functional theory (DFT). Simplified contact models allow a qualitative investigation of both the influence of geometry and CNT length, and the strength and extent of the contact on the transport properties. In addition, such simple contact models are used to compare the influence of different electronic structure methods on transport. It is found that the semiempirical TB and EHT are inadequate to quantitatively reproduce the DFT-based results. Based on this observation, an improved set of Hückel parameters is developed, which remedies this insufficiency. A systematic investigation of different contact materials is carried out using well defined atomistic metal-CNT-metal structures, optimized in a systematic way. Analytical models for the CNT-metal interaction are proposed. Based on that, electronic transport calculations are carried out, which can be extended to large systems by applying the computationally cheap improved EHT. The metal-CNT-metal systems can then be ranked by average conductance: Ag ≤ Au < Cu < Pt ≤ Pd < Al. This corresponds qualitatively with calculated contact distances, binding energies and work functions of CNTs and metals. To gain a deeper understanding of the transport properties, the electronic structure of the metal-CNT-metal systems and their respective parts is analyzed in detail. Here, the energy resolved local density of states is a valuable tool to investigate the CNT-metal interaction and its influences on the transport.
Die kontinuierliche Verkleinerung der Strukturgrößen stellt hohe Anforderungen an Materialen und Technologien zukünftiger hochintegrierter Schaltkreise. Insbesondere die Leistungsfähigkeit kupferbasierte Leitbahnsystem wird bald an fundamentale Grenzen stoßen. Aufgrund ihrer hervorragenden Eigenschaften könnten metallische Kohlenstoffnanoröhren (engl. Carbon Nanotubes, CNTs) Kupfer in zukünftigen Leitbahnsystemen teilweise ersetzen. Dabei ist ein geringer Kontaktwiderstand mit vorhandenen Leitbahnen von entscheidender Bedeutung. Die vorliegende Arbeit liefert grundlegende Beiträge zur Theorie und zur numerischen Beschreibung elektronischer Transporteigenschaften metallischer CNTs mit Metallkontakten. Dazu werden verschiedene theoretische Ansätze auf diverse Kontaktmodelle angewandt und eine Auswahl von Elektrodenmaterialen (Al, Cu, Pd, Ag, Pt, Au) verglichen. Die Beschreibung ballistischen Elektronentransports erfolgt mittels des Formalismus der Nichtgleichgewichts-Green-Funktionen in Kombination mit Tight-Binding (TB), erweiterter Hückel-Theorie (EHT) und Dichtefunktionaltheorie (DFT). Vereinfachte Kontaktmodelle dienen der qualitativen Untersuchung des Einflusses von Geometrie und Länge der Nanoröhren, sowie von Stärke und Ausdehnung des Kontaktes. Darüber hinaus erlauben solch einfache Modelle mit geringem numerischen Aufwand den Einfluss verschiedener Elektronenstrukturmethoden zu untersuchen. Es zeigt sich, dass die semiempirischen Methoden TB und EHT nicht in der Lage sind die Ergebnisse der DFT quantitativ zu reproduzieren. Ausgehend von diesen Ergebnissen wird ein verbesserter Satz von Hückel-Parametern generiert, der diesen Mangel behebt. Die Untersuchung verschiedener Kontaktmaterialien erfolgt an wohldefinierten atomistischen Metall-CNT-Metall-Strukturen, welche systematisch optimiert werden. Analytische Modelle zur Beschreibung der CNT-Metall-Wechselwirkung werden vorgeschlagen. Darauf aufbauende Berechnungen der elektronischen Transporteigenschaften, können mit Hilfe der verbesserten EHT auf große Systeme ausgedehnt werden. Die Ergebnisse ermöglichen eine Reihung der Metall-CNT-Metall-Systeme hinsichtlich ihrer Leitfähigkeit: Ag ≤ Au < Cu < Pt ≤ Pd < Al. Dies korrespondiert qualitativ mit berechneten Kontaktabständen, Bindungsenergien und Austrittarbeiten der CNTs und Metalle. Zum tieferen Verständnis der Transporteigenschaften erfolgt eine detaillierte Analyse der elektronischen Struktur der Metall-CNT-Metall-Systeme und ihrer Teilsysteme. Dabei erweist sich die energieaufgelöste lokale Zustandsdichte als nützliches Werkzeug zur Visulisierung und zur Charakterisierung der Wechselwirkung zwischen CNT und Metall sowie deren Einfluss auf den Transport.

Carbon nanotubes (CNTs) are promising nanomaterials for high frequency applications due to their unique physical characteristics. CNTs have a low heat capacity, low intrinsic capacitance, and incredibly fast thermal time constants. They can also exhibit ballistic transport at low bias, for both phonons and electrons, as evident by their fairly long mean free paths. However, despite the great potential they present, the RF behavior of these nanostructures is not completely understood. In order to explore this high frequency regime we studied the microwave (MW) and terahertz (THz) response of individual and bundled single wall nanotube based devices. This thesis is an experimental study which attempts to understand the high frequency characteristics of metallic single walled carbon nanotubes, and to develop an ultra-fast and sensitive direct THz detector. First, the appropriate high frequency detector background is introduced. CNTs previously measured behavior draws similarities to two types of detectors: diode and bolometer. Therefore, our CNT devices are geared towards those designs. Second the fabrication process of devices is reviewed. UV lithography is used to pattern THz coupling log periodic antennas, on top of which CNTs are deposited by using a dielectrophoretic process. Third, the fabricated devices are tested at DC, MW, and THz frequencies. All of these measurements are done as a function of temperature, power, and frequency. Finally, the physical processes that give rise to the diode and bolometric detections at MW and THz detection at different temperatures and under different bias regimes (i.e. low and high) are explained.

It is reported that terahertz radiation from 0.69 to 2.54 THz has been sensitively detected in a device consisting of bundles of carbon nanotubes containing single wall metallic carbon nanotubes, quasi-optically coupled through a lithographically fabricated antenna, and a silicon lens. The measured data are consistent with a bolometric detection process in the metallic tubes and the devices show promise for operation well above 4.2 K. Microwave measurements have also been done up to 20GHz. Voltage responsivity got here is comparable to that of the Schottky diode detector. The detection at microwave frequencies are consistent with the diode detection mode. S11 parameters of different devices were measured using microwave probing, and de-embedding process has been done to get the impedances of the SWNTs. A circuit model was fitted based on the measurement data, and different values of the elements of the circuit are extracted. Frequency response from the circuit model is consistent with the experimental data.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.
Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6455. Adviser: Karl Hess. Includes bibliographical references (leaves 86-88) Available on microfilm from Pro Quest Information and Learning.

碩士
國立中興大學
化學工程學系
93
Owing to the properties of lower density, larger specific surface area, unique structure and adsorption, carbon nanotubes (CNTs) has become attractive and extensively applied in many researcher groups. In recent literatures, it has an excellent application in catalysis to use CNTs as a support in different catalytic reactions. In this study, CNTs are used as a support, and the supported metal oxide catalysts are prepared by impregnation method to perform with the propane oxidation reaction. Upon the surface treatment on CNTs, the original catalysts and the amorphous carbon on CNTs can be removed efficiently and the purity of CNTs can be improved, specific surface area of CNTs and carboxyl groups can be increased and produced to make CNTs more hydrophilic. To analyze the effect of different contents of supported metal (vanadium, molybdenum and chromium) oxide on the CNTs, BET surface area, TGA, XRD and Raman will be used to characterize the structural information of CNTs. From the results, the surface metal oxides may be formed as V2O5, Cr2O3 and MoO3 crystallites, and metal oxide layers on CNTs surface can be coexisted on the CNTs surface. The concentration of reaction products was detected by GC analysis and determine that the products are propene and by-products, such as CO, CO2, CH4, C2H6 etc. In the catalytic results, the supported chromium oxide catalysts possess a higher conversion and yields among the supported metal oxide catalysts. However, the supported molybdenum oxide catalysts possess a higher selectivity. By increasing temperature, the reaction conversion increases and selectivity goes lower. With the increase of the oxygen feed ratio, the by-products CO and CO2 become increasing. In addition, the propane conversion increases with increasing surface metal oxide concentration in the catalysts and drop off with further increasing the coverage of surface metal oxide. Thus, the catalyst properties are related to the concentrations of metal oxide additive. In the propane oxidation reaction, the thermal stability of CNTs used as a support is higher than those on active carbon support, and furthermore, it possesses higher catalytic effect at higher temperature condition.

Tese de doutoramento em Engenharia Mecânica, na especialidade de Nanomateriais e Microfabricação, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
In the last decades, the metal powder injection moulding (MIM), in its different versions – micro MIM technology, is a manufacturing process consolidated as an effective and competitive alternative to produce small size and complex geometry of metallic parts in large scale, with high quality and reproducibility. The remarkable expansion in different industrial sectors requires a re-adaptation to new materials with new functionalities, like nanocomposites. This thesis focuses on the processing by µMIM technology of nanocomposites of SS 316L powders nanoreinforced with multi wall carbon nanotube (MWCNT). The challenge of the work is to guarantee a homogeneous distribution of MWCNT in the matrix, produce nanocomposites feedstocks with suitable rheological characteristics (to guarantee the injection moulding) and to maintain the MWCNT content whatever the steps of processing (debinding and sintering). Afterward, to optimise the mechanical properties of SS 316L nanocomposites. Firstly, the optimization of the feedstocks as well all the conditions were made to SS 316L matrix without nanoreinforcement addition (called master feedstocks – MF). The feedstock with the SS 316L powders and the commercial binder (M1), have been optimized. The production and characterization of the feedstocks is carried out through mixing torque tests, and density/ morphology respectively. The SS 316L feedstock had always a lower torque value than feedstock with other metal powders (e. g. copper) with same 2Ss (particle size and particle size distribution). The addition of different percentages (0.8, 1.7, 2.5 and 3.3% vol.) of nanoreinforcements increases always the torque value of feedstocks, whatever the matrix and the nanoreinforcement type (nanotubes or nanoparticles). Considering the high torque values, the addition of stearic acid proved to be essential for lowering the torque values and making the blends processable by injection moulding. The injection moulding was performed in a microinjection machine and the optimization of the parameters were made firstly for feedstock without nanoreinforcement – MF. The injection pressure used is the transition value between low and high pressure. With increasing nanoreinforcement content, the flowability decreases and the injection parameters must be adjusted to guarantee a complete filling of moulding cavity. The thermal debinding cycle was defined based on thermal analysis of M1. The binder removal rate was between 94 – 96 % for all the green components tested. After debinding step, no defects were found from this step. The MF was sintered at different temperatures (1150, 1200, 1250 and 1300 ºC) with aim of perceiving the influence of the sintering temperature. The SS 316L composites nanoreinforced with MWCNT were sintered at sintering temperature which shown best results: 1250 ºC, during 60 minutes, under controlled atmosphere. The sintering temperature showed to have some influence on the final properties of the sintered ones. The porosity presents acceptable values for the technique used (less than 5%) and the hardness presents higher values for higher sintering temperatures. In contrast, the Young’s modulus decreases with temperature. For all the conditions tested (%vol. of MWCNT and sintering temperature), the shrinkage of MMC component varied from 10 to 16.5%. What concern to %vol. of MWCNT (when this increases) the density shows an increased value that varying between 93 % and 97 %. Increasing the %vol. MWCNT, the hardness values showed an increase of 39% (with 3.3 %vol.) compared to MF, sintered in same conditions. What concern to YS values, increase with the addition of nanotubes, while the addition of 3.3 %vol. represents an increase of 76%, compared to 0.0 %vol.. With respect to the wrought material, the addition of 3.3 %vol. to composite presents higher values in hardness and UTS. The fracture surface of the mechanically tested samples was evaluated and the presence of the nanotubes was verified by SEM and TEM. The brown samples, reinforced with 1.7 and 3.3% vol. were coated with a thin film, with the aim of preventing the degradation of the MWCNTs during the thermal sintering process.
Nas últimas décadas, a moldação por injeção de pós metálicos (MIM), na sua variante - microMIM, é um processo de fabrico consolidado e uma alternativa competitiva para produzir peças metálicas de geometria complexa e pequeno tamanho e em grande escala, com elevada qualidade e reprodutibilidade. A notável expansão em diferentes setores industriais requer uma readaptação a novos materiais, com novas funcionalidades, como nanocompósitos. Esta tese concentra-se no processamento de nanocompósitos de pós SS 316L nanorreforçados com nanotubos de carbono de parede múltipla (MWCNT), pela tecnologia de microMIM. O desafio deste trabalho é garantir uma homogénea distribuição dos MWCNT na matriz, produzir feedstocks nanocompósitos com características reológicas adequadas (para garantir a moldagem por injeção) e manter o teor de MWCNT, independentemente das etapas de processamento (remoção do ligante e sinterização). Por fim, otimizar as propriedades mecânicas dos nanocompósitos de SS 316L. Primeiramente, foi realizada a otimização dos feedstocks, bem como de todas as condições a os pós de SS 316L, sem adição de nanorreforço (denominado master feedstock - MF). As misturas com os pós de SS 316L e o ligante comercial (M1) foram otimizadas. A produção e caracterização dos feedstocks foi realizada respetivamente através de testes de reometria de binário e densidade/morfologia. O feedstock de SS 316L tem um binário inferior a feedstocks com outros pós metálicos (por exemplo, cobre) com o mesmo 2S (tamanho de partícula e distribuição de tamanho de partícula). A adição de diferentes percentagens (0.8, 1.7, 2.5 e 3.3% vol.) de nanorreforço aumenta sempre o valor do binário dos feedstocks, seja qual for a matriz e o tipo de nanorreforço (nanotubos ou nanopartículas). Considerando os elevados valores do torque, a adição de ácido esteárico revelou-se fundamental para baixar os valores do torque e tornar as misturas processáveis por moldação. A moldagem por injeção foi realizada numa microinjetora e a otimização dos parâmetros foi realizada para o feedstock sem nanorreforço - MF. A pressão de injeção utilizada é considerada a fronteira entre baixa e alta pressão. Com o aumento do teor de nanorreforço, a fluidez diminui e os parâmetros de injeção devem ser ajustados para garantir um completo preenchimento da cavidade moldante. O ciclo de remoção térmico do ligante foi definido com base analise térmica do M1. A taxa de remoção do ligante foi entre 94 – 96%, para todos os componentes verdes testados. Após a etapa de remoção do ligante, não foram encontrados defeitos nos componentes provenientes desta etapa. O MF foi sinterizado a diferentes temperaturas (1150, 1200, 1250 e 1300 ºC) com o objetivo de perceber a influência da temperatura de sinterização. Os SS 316L compósitos nanorreforçados com MWCNT foram sinterizados à temperatura de sinterização que apresentou melhores resultados: 1250 ºC, durante 60 minutos, sob atmosfera controlada. A temperatura de sinterização mostrou ter alguma influência nas propriedades finais dos sinterizados. A porosidade apresenta valores aceitáveis para a técnica utilizada (inferior a 5%) e a dureza apresenta valores maiores para maiores temperaturas de sinterização. Em contraste, o módulo de Young diminui com a temperatura. Para todas as condições testadas (%vol. de MWCNT e temperatura de sinterização), a retração dos componentes MMC variou de 10 a 16,5%. Relativamente à %vol. de MWCNT (quando esta aumenta), a densidade apresenta um aumento crescente, que varia entre 93% e 97%. O aumento do teor de MWCNT, revela um aumento de dureza na ordem dos 39% (com 3,3 %vol.) comparativamente com o MF sinterizado nas mesmas condições. Relativamente aos valores de YS, aumentam com a adição de nanotubos, representando um aumento de 76% com a adição de 3,3 %vol., em comparação com 0,0 %vol. No que diz respeito ao material de referência, a adição de 3,3 %vol. ao compósito induz num aumento de dureza e UTS. A superfície de fratura das amostras testadas mecanicamente foi avaliada e a presença dos nanotubos foi constatada por SEM e TEM. As amostras castanhas, reforçadas com 1,7 e 3,3% vol. foram revestidos com uma fina camada, com o objetivo de evitar a degradação dos MWCNT durante o processo de sinterização térmica.

An mathematical expression has been derived and analysed for total potential energy V and field emission current density function ϕ of emitted electrons by taking into account the distribution of charge along the length of the carbon nanotubes (CNTs), matching to the representation for the tunnelling coefficient. This tunnelling coefficient is obtained from solving of the time independent Schrödinger’s wave equation. Mathematical calculations for the potential energy V, tunnelling coefficient T and current density function ϕ have been worked out for a distinctive set of the CNTs factors. It is concluded that the potential energy in ergs declines with the radial distance r but increases with z coordinate along the length of the CNT. Moreover, the current density function at the spherical CNT tip is substantially larger than along the length of cylindrical metallic CNT. In addition, the field emission current density function decreases with radius of CNTs in both the cases (i.e., cylindrical and spherical tip). Some of our theoretical results are in agreement with the current experimental observations.

Due to the aggressive downscaling of the CMOS technology, power and current densities are increasing inside the chip. The limiting current conduction capacity(106 Acm−2)and thermal conductivity(201Wm−1K−1 for Al and 400 Wm−1K−1 for Cu) of the existing interconnects materials has given rise to different electro-thermal issues such a shot-spot formation, electromigration, etc. Exploration of new materials with high thermal conductivity and current conduction has thus attracted much attention for future integrated circuit technology. Among all the elemental materials, carbon nanomaterials (graphene and carbon nanotube) possess exceptionally high thermal (600-7000 Wm−1K−1) and current( ~108 -109 Acm−2)conduction properties at room temperature, which makes them potential candidate for interconnect materials. At the same time development of efficient energy harvesting techniques are also becoming important for future wireless autonomous devices. The excess heat generated at the hot-spot location could be used to drive an electronic circuit through a suitable thermoelectric generator. As the See beck coefficient of graphene is reported to be the highest among all elementary semiconductors, exploration of thermoelectric properties of graphene is very important. This thesis investigates the electrothermal and thermoelectric properties of metallic single walled carbon nanotube (SWCNT) and single layer graphene (SLG) for their possible applications in thermal management in next generation integrated circuits. A closed form analytical solution of Joule-heating equation in metallic SWCNTs is thus proposed by considering a temperature dependent lattice thermal conductivity (κ) on the basis of three-phonon Umklapp, mass-difference and boundary scattering phenomena. The solution of which gives the temperature profile over the SWCNT length and hence the location of hot-spot(created due to the self-heating inside the chip) can be predicted. This self-heating phenomenon is further extended to estimate the electromigration performance and mean-time-to-failure of metallic SWCNTs. It is shown that metallic SWCNTs are less prone to electromigration. To analyze the electro-thermal effects in a suspended SLG, a physics-based flexural phonon dominated thermal conductivity model is developed, which shows that κ follows a T1.5 and T−2 law at lower(<300 K) and higher temperature respectively in the absence of isotopes(C13 atoms). However in the presence of isotopic impurity, the behavior of κ sharply deviates from T−2 at higher temperatures. The proposed model of κ is found to be in excellent match with the available experimental data over a wide range of temperatures and can be utilized for an efficient electro-thermal analysis of encased/supported graphene. By considering the interaction of electron with in-plane and flexural phonons in a doped SLG sheet, a physics-based electrical conductance(σ) model of SLG under self-heating effect is also discussed that particularly exhibits the variation of electrical resistance with temperature at different current levels and matches well with the available experimental data. To investigate the thermoelectric performance of a SLG sheet, analytical models for See beck effect coefficient (SB) and specific heat (Cph) are developed, which are found to be in good agreement with the experimental data. Using those analytical models, it is predicted that one can achieve a thermoelectric figure of merit(ZT) of ~ 0.62 at room temperature by adding isotopic impurities(C13 atoms) in a degenerate SLG. Such prediction shows the immense potential of graphene in waste-heat recovery applications. Those models for σ, κ, SB and Cph are further used to determine the time evolution of temperature distribution along suspended SLG sheet through a transient analysis of Joule-heating equation under the Thomson effect. The proposed methodology can be extended to analyze the graphene heat-spreader theory and interconnects and graphene based thermoelectrics.

Due to the aggressive downscaling of the CMOS technology, power and current densities are increasing inside the chip. The limiting current conduction capacity(106 Acm−2)and thermal conductivity(201Wm−1K−1 for Al and 400 Wm−1K−1 for Cu) of the existing interconnects materials has given rise to different electro-thermal issues such a shot-spot formation, electromigration, etc. Exploration of new materials with high thermal conductivity and current conduction has thus attracted much attention for future integrated circuit technology. Among all the elemental materials, carbon nanomaterials (graphene and carbon nanotube) possess exceptionally high thermal (600-7000 Wm−1K−1) and current( ~108 -109 Acm−2)conduction properties at room temperature, which makes them potential candidate for interconnect materials. At the same time development of efficient energy harvesting techniques are also becoming important for future wireless autonomous devices. The excess heat generated at the hot-spot location could be used to drive an electronic circuit through a suitable thermoelectric generator. As the See beck coefficient of graphene is reported to be the highest among all elementary semiconductors, exploration of thermoelectric properties of graphene is very important. This thesis investigates the electrothermal and thermoelectric properties of metallic single walled carbon nanotube (SWCNT) and single layer graphene (SLG) for their possible applications in thermal management in next generation integrated circuits. A closed form analytical solution of Joule-heating equation in metallic SWCNTs is thus proposed by considering a temperature dependent lattice thermal conductivity (κ) on the basis of three-phonon Umklapp, mass-difference and boundary scattering phenomena. The solution of which gives the temperature profile over the SWCNT length and hence the location of hot-spot(created due to the self-heating inside the chip) can be predicted. This self-heating phenomenon is further extended to estimate the electromigration performance and mean-time-to-failure of metallic SWCNTs. It is shown that metallic SWCNTs are less prone to electromigration. To analyze the electro-thermal effects in a suspended SLG, a physics-based flexural phonon dominated thermal conductivity model is developed, which shows that κ follows a T1.5 and T−2 law at lower(<300 K) and higher temperature respectively in the absence of isotopes(C13 atoms). However in the presence of isotopic impurity, the behavior of κ sharply deviates from T−2 at higher temperatures. The proposed model of κ is found to be in excellent match with the available experimental data over a wide range of temperatures and can be utilized for an efficient electro-thermal analysis of encased/supported graphene. By considering the interaction of electron with in-plane and flexural phonons in a doped SLG sheet, a physics-based electrical conductance(σ) model of SLG under self-heating effect is also discussed that particularly exhibits the variation of electrical resistance with temperature at different current levels and matches well with the available experimental data. To investigate the thermoelectric performance of a SLG sheet, analytical models for See beck effect coefficient (SB) and specific heat (Cph) are developed, which are found to be in good agreement with the experimental data. Using those analytical models, it is predicted that one can achieve a thermoelectric figure of merit(ZT) of ~ 0.62 at room temperature by adding isotopic impurities(C13 atoms) in a degenerate SLG. Such prediction shows the immense potential of graphene in waste-heat recovery applications. Those models for σ, κ, SB and Cph are further used to determine the time evolution of temperature distribution along suspended SLG sheet through a transient analysis of Joule-heating equation under the Thomson effect. The proposed methodology can be extended to analyze the graphene heat-spreader theory and interconnects and graphene based thermoelectrics.

The hybrid nanostructures exhibit excellent performances in various fields such as catalysis, sensing, and energy conversion as compared to their individual ones. The thesis deals with the new methods for the synthesis of different type of hybrids with doped/pristine carbon nanostructures in the form of graphene, multiwall carbon nanotubes (MWCNTs) as one component and metals nanostructures (Ag, Pd, Pt and Au), carbide (Fe3C), metal chalcogenides (Ni3S2 and Co9S8) and oxide (CoO) as the other components. Various synthesis techniques such as modified galvanic replacement reaction at room temperature, hydrothermal, microwave and pyrolysis have been explored for the synthesis of different hybrid nanostructures. Furthermore, various hybrid nanostructures have been explored for various catalytic activities such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and 4-nitrophenol (4-NP) reduction. It may be noted that the ORR and OER which are undoubtedly vital for their applications in fuel cells, metal-air batteries and water oxidation reaction. Interestingly, the catalytic activities of these hybrid nanostructures are comparable or better as compared to the commercial benchmark precious catalysts.

The hybrid nanostructures exhibit excellent performances in various fields such as catalysis, sensing, and energy conversion as compared to their individual ones. The thesis deals with the new methods for the synthesis of different type of hybrids with doped/pristine carbon nanostructures in the form of graphene, multiwall carbon nanotubes (MWCNTs) as one component and metals nanostructures (Ag, Pd, Pt and Au), carbide (Fe3C), metal chalcogenides (Ni3S2 and Co9S8) and oxide (CoO) as the other components. Various synthesis techniques such as modified galvanic replacement reaction at room temperature, hydrothermal, microwave and pyrolysis have been explored for the synthesis of different hybrid nanostructures. Furthermore, various hybrid nanostructures have been explored for various catalytic activities such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and 4-nitrophenol (4-NP) reduction. It may be noted that the ORR and OER which are undoubtedly vital for their applications in fuel cells, metal-air batteries and water oxidation reaction. Interestingly, the catalytic activities of these hybrid nanostructures are comparable or better as compared to the commercial benchmark precious catalysts.

碩士
國立高雄大學
土木與環境工程學系碩士班
97
This study was focused tradition electrokinetic technology, it only except pollutant, but not degrade and destroy it. Using binary metallic oxide electrode combine the electrokinetic (BMOE-EK) technology to regeneration carbon nanotubs. It can effective to solve pollution, shortening completely to go on, will make traditional electrokinetic technology become the new technology that the environment continues the characteristic forever. Test regeneration and absorb enduring the carbon nanotubes and is in charge of of saturation nonylphenol, consider the electrode kind in electrokinetic, it influences the parameter to operate liquid kind, electric potential slope lowering, operating time,etc., Dr.eye: probe into it and get rid of the mechanism and recycled efficiency. Probe into the liquid and take a fancy to NP and endure the behavior of absorbing that the carbon nanotubes is in charge of at first, the result shows pH value was decreased and the absorbing amount is the higher. When 2.5 mg/L and pH 4 in NP, the absorbing amount can reach 353.4 mg/g after 14 hr. After imitating and returning to operation after waiting for and absorbing the experiment warmly, is it endure carbon nanotubes in charge of to wait for warm to is it is it wait with BET warm to absorb equation preface to accord with relatively to absorb NP to show; Learn by absorbing the equation preface simulation of motive force, originally absorb and test and follow and draft two stepses of motive force equation preface. Electrode prepared of this experiment, carrying on the treatment of 8 hr in 1V/cm, its C used to degrade the result and traditional electrokinetic makes and relatively makes and can a multiple 1.68 of treatment results for the electrode looks of anode excellently, it is excellent to represent it of one BMOE and degrade carbon nanotubes that efficiency is far greater than the law of traditional electrokinetic. Learn experimental result operate by liquid being at electrode for at the time of RuO2/Ti different operation liquid degrade efficiency of been for degrading influence of efficiency including: Sodium chloride (69.0%) >NaOH (54.8%) >Citric acid (48.7%) ,It show have getting better more relatively results at being for operate liquiding at sodium chloride, not may sodium chloride produce OCl of in the electrolytic course -, it have strong person who oxidize, have OCl at the same time - and the oxyhydrogen free radical can degrade the base phenol of Ren effectively, than operate liquid degrade Ren to be base phenol result good for NaOH by oxyhydrogen free radical. The amount of TOC utilized examines and endures the carbon nanotubes NP ore rate that manages with quantization BMOE-EK technological regeneration, the result shows ore rates are more than 65%, represent a pair of metal and oxidize the oxidizing certain effect to NP of electrode. It is in charge of utilizing regeneration of law of electrokinetic to have feasibility demonstrating and enduring the carbon nanotubes at the same time. Compare PbO2/Ti, PbO2-Co/Ti and PbO2/SnO2 +Sb2O3/Ti to find from the liquid of operating in this experiment, PbO2/Ti is easy to peel off the citric acid, cause slightly bad to on PbO2/SnO2 +Sb2O3/Ti, make Cheng put Co2+ can promote their nonylphenol degrade the result in PbO2/Ti result its. Absorb the liquid phase repeatedly by absorbing enduring the carbon nanotubes and is in charge of of saturation nonylphenol - take off the experiment of enclosing, CNT absorbing amount still about absorb 96.2% for the first time in 340 mg/g, show that endures the carbon nanotubes and is in charge of re-utilizing nature after 10 times by regeneration, it has high economic benefits. The result shows that, while combining the regeneration of electrokinetic and enduring the carbon nanotubes and is in charge of with one pair of metal electrodes, can promote and endure the recycled efficiency that the carbon nanotubes is in charge of by operating the selecting and selecting of the liquid and electrode material condition.

Single-Walled Carbon Nanotube (SWCNT) based Very Large Scale Integrated circuit (VLSI) interconnect is one of the emerging technologies, and has the potential to overcome the thermal issues persisting even with the advanced copper based interconnect. This is because of it’s promising electrical and thermal transport properties. It can be stated that thermal energy transport in SWCNTs is highly anisotropic due to the quasi one dimensionality, and like in other allotropes of carbon, phonons are the dominant energy carriers of heat conduction. In case of conventional interconnect materials, copper and aluminium, although their thermal conductivity varies over orders of magnitude at temperatures below100 K, near room temperature and above they have almost constant value. On the other hand, the reported experimental studies on suspended metallic SWCNTs illustrate a wide variation of the longitudinal lattice thermal conductivity (κl) with respect to the temperature(T)and the tube length(L)at low, room and high temperatures. Physics based analytical formulation of κl of metallic SWCNT as a function of L and T is essential to efficiently quantify this emerging technology’s impact on the rising thermal management issues of Integrated Circuits. In this work, a physics based diameter independent analytical model for κl of metallic SWCNT is addressed as a function of Lover a wide range of T. Heat conduction in metallic SWCNTs is governed by three resistive phonon scattering processes; second order three phonon Umklapp scattering, mass difference scattering and boundary scattering. For this study, all the above processes are considered, and the effective mode dependent relaxation time is determined by the Matthiessen’s rule. Phonon Boltzmann transport equation under the single mode relaxation time approximation is employed to derive the non-equilibrium distribution function. The heat flux as a function of temperature gradient is obtained from this non-equilibrium distribution function. Based on the Fourier’s definition of thermal conductivity, κl of metallic SWCNT is formulated and the Debye approximations are used to arrive at analytical model. The model developed is validated against both the low and high temperature experimental investigations. At low temperatures, thermal resistance of metallic SWCNT is due to phonon-boundary scattering process, while at high temperatures it is governed by three phonon Umklapp scattering process. It is understood that apart from form factor due to mass difference scattering, boundary scattering also plays the key role in determining the peak value. At room temperature, κl of metallic SWCNT is found to be an order of magnitude higher than that of most of metals. The reason can be attributed to the fact that both sound velocity and Debye temperature which have direct effect on the phonon transport in a solid, are reasonably higher in SWCNTs. Though Umk lapp processes reduce the κl steeper than 1/T beyond room-temperature, it’s magnitude is round1000 W/m/K upto 800 K for various tube lengths, which confirms that this novel material is indeed an efficient conductor of heat also, at room-temperature and above.

Single-Walled Carbon Nanotube (SWCNT) based Very Large Scale Integrated circuit (VLSI) interconnect is one of the emerging technologies, and has the potential to overcome the thermal issues persisting even with the advanced copper based interconnect. This is because of it’s promising electrical and thermal transport properties. It can be stated that thermal energy transport in SWCNTs is highly anisotropic due to the quasi one dimensionality, and like in other allotropes of carbon, phonons are the dominant energy carriers of heat conduction. In case of conventional interconnect materials, copper and aluminium, although their thermal conductivity varies over orders of magnitude at temperatures below100 K, near room temperature and above they have almost constant value. On the other hand, the reported experimental studies on suspended metallic SWCNTs illustrate a wide variation of the longitudinal lattice thermal conductivity (κl) with respect to the temperature(T)and the tube length(L)at low, room and high temperatures. Physics based analytical formulation of κl of metallic SWCNT as a function of L and T is essential to efficiently quantify this emerging technology’s impact on the rising thermal management issues of Integrated Circuits. In this work, a physics based diameter independent analytical model for κl of metallic SWCNT is addressed as a function of Lover a wide range of T. Heat conduction in metallic SWCNTs is governed by three resistive phonon scattering processes; second order three phonon Umklapp scattering, mass difference scattering and boundary scattering. For this study, all the above processes are considered, and the effective mode dependent relaxation time is determined by the Matthiessen’s rule. Phonon Boltzmann transport equation under the single mode relaxation time approximation is employed to derive the non-equilibrium distribution function. The heat flux as a function of temperature gradient is obtained from this non-equilibrium distribution function. Based on the Fourier’s definition of thermal conductivity, κl of metallic SWCNT is formulated and the Debye approximations are used to arrive at analytical model. The model developed is validated against both the low and high temperature experimental investigations. At low temperatures, thermal resistance of metallic SWCNT is due to phonon-boundary scattering process, while at high temperatures it is governed by three phonon Umklapp scattering process. It is understood that apart from form factor due to mass difference scattering, boundary scattering also plays the key role in determining the peak value. At room temperature, κl of metallic SWCNT is found to be an order of magnitude higher than that of most of metals. The reason can be attributed to the fact that both sound velocity and Debye temperature which have direct effect on the phonon transport in a solid, are reasonably higher in SWCNTs. Though Umk lapp processes reduce the κl steeper than 1/T beyond room-temperature, it’s magnitude is round1000 W/m/K upto 800 K for various tube lengths, which confirms that this novel material is indeed an efficient conductor of heat also, at room-temperature and above.

碩士
元智大學
化學工程與材料科學學系
97
This research was divided into two parts to explore. In the part 1, we used three different reduction methods to prepare the same ratios of Pt–Co/CNT catalysts. In the part 2, we used the method of microwave reduction to prepare three kinds of proportion of Pt–Co/MCMB catalysts. Part 1: The electrochemical activities of three types of Pt–Co/CNT catalysts, prepared from different Co depositions, in methanol oxidation have been investigated. X-ray diffraction reveals that these Pt–Co/CNT catalysts possess not only different crystalline sizes but also different levels of atomic distribution. The use of strong reducing agent (NaBH4) enables the formation of a cobalt layer over the Pt surface, inducing bimetallic Pt–Co particles, whereas direct thermal reduction enables the formation of Pt–Co nanoalloy with a high degree of alloying. It has been shown that the normalized active surface coverage increases the alloying degree of Pt–Co catalysts, indicating the importance of atomic distribution. Cyclic voltammetric measurement also reveals that the Pt–Co/CNT catalyst with a good alloying degree exhibits a better electrochemical activity, high CO tolerance, and long-term durability (> 100 cycles). This activity improvement in methanol oxidation can be attributed to the bifunctional mechanism of binary catalysts: since the Pt–Co/CNT catalyst offers a large amount of Pt–Co pairs, the Co site serves as a promoting center for the generation of Co–OH species, and thus more Pt sites are available for methanol oxidation. Accordingly, the synthesis condition is one of the key factors affecting the distribution of surface atoms, significantly related to their catalytic ability in methanol oxidation. Part 2: The method of microwave reduction was used to prepare Pt–Co/MCMB catalysts with different Pt/Co atomic ratios. It revealed that three kinds of catalysts, Pt25Co75/MCMB, Pt50Co50/MCMB and Pt75Co25/MCMB, exhibit different crystal sizes showing different electrochemical activities in methanol oxidation. From CV curve, the electrochemical surface area is the decrease function of scan number. The Pt50Co50/MCMB catalyst displays the best electrochemical properties among the Pt-Co/MCMB catalysts, revealing importance of different proportion. In the methanol oxidization, IF/IB value of Pt25Co75/MCMB, Pt50Co50/MCMB and Pt75Co25/MCMB are 1.08, 1.12 and 1.13 after 100 cycles, respectively. We inference the particle size of the method of microwave reduction to affect the electrochemical activity is one of importance factors, and the method of microwave reduction can substantial decrease reduction time.

碩士
國立雲林科技大學
環境與安全工程系碩士班
94
High BOD, COD, temperature and coloring of dye-house effluents are generally cleaned by combining biodegradation and physical-chemical treatment to improve degradation rate. However, these processes produce large quantities of waste sludges. Many researchers propose UV/TiO2 process to treat those dye-house effluents and to effectively de-color and mineralize dye. In this study, two types of composite materials, Fe-Ni/TiO2 powders and TiO2/CNT were fabricated and were used as photo-catalysts in UV/TiO2¬ process. And, chromium ions (Cr+6) were added as electron scavenger to study the simultaneous and synergistic conversion in UV/TiO2¬ process. To characterize the crystalline structure of the powders, the XRD and TEM patterns of Fe-Ni/TiO2, TiO2/CNT composites, TiO2 and MWCNT are tested. The sol-gel production method successfully deposited TiO2 onto CNTs surface, and the existence of CNTs would interfere the growth and particle sizes of TiO2 . However, the XRD patterns did not observe graphite phase of CNTs—a phenomenon that probably indicated the coverage effects(the main graphite peak of CNTs overlapped with the main peak of anatase). The specific areas of TiO2/CNT, sol-gel TiO2, Degussa P25 and Fe-Ni/TiO2 are 106.4, 104, 47.05 and 12.33 m2/g. In the adsorption tests, Fe-Ni nanoparticles on TiO2 don’t enhance the adsorption ability and the CNTs did enhance the adsorption ability of TiO2. The adsorption capacities after 12 hours are 35.03 mg/g (Fe-Ni/P25, Fe-Ni/TiO2), 43.44 mg/g (TiO2/CNT 10:1) and 45.54 mg/g (TiO2/CNT 5:1).Using TiO2/CNT (10:1) to degrade AO7 could reach 73% and reduce the total organic carbon (TOC) from 7.09 ppm to 3.8 ppm by UV lamp 60 W (among 30, 60 and 90 W). Studying synergetic effects in UV/TiO2/Cr+6 system, the removal rates reduced by using Degussa P25 and TiO2/CNT while increase by sol-gel TiO2 and no effect by Fe-Ni/TiO2 at the present of Cr+6.

Einwandige Kohlenstoffnanoröhrchen wurden aufgrund ihrer einzigartigen elektrischen, mechanischen und thermischen Eigenschaften 1991 in den Fokus der Forschung gerückt. In dieser Dissertation wird gezeigt, dass Ramanspektroskopie eine der besten Methoden ist, um die unterschiedlichen Eigenschaften der Nanoröhrchen wie ihren elektrischen Charakter (halbleitend oder metallisch), ihren Durchmesser, die Chiralität, Defekte oder auch Dotierung zu untersuchen. Die Charakterisierung dieser Eigenschaften wird sowohl für das reine Material als auch im elektrischen Bauteil, in diesem Fall einem Feldeffekttransistor, durchgeführt. Der erste Teil der Arbeit vermittelt einen Überblick und gibt eine Einführung in Ramanspektroskopie und in die Struktur von Kohlenstoffnanoröhrchen. Es wird erklärt, welche Eigenschaften speziell mit Hilfe von Position und Intensität der Raman-Modi untersucht werden können und welche Aussagen über die Eigenschaften getroffen werden können. Im experimentellen Teil der Arbeit wurde eine Methode entwickelt, die eine rückstandslose Abscheidung von Dünnschichten aus Kohlenstoffnanoröhrchen ermöglicht. Die Quantifizierung von Defekten wurde durch die in den untersuchten Proben vorhandenen metallischen und halbleitenden Kohlenstoff-Nanoröhrchen ermöglicht. Mittels spitzenverstärkter Ramanspektroskopie wurden außerdem Defekte mit hoher Ortsauflösung (unterhalb von 10 nm) an einzelnen Nanoröhrchen charakterisiert. Der letzte Teil widmet sich den Eigenschaften in elektrische Bauteile, speziell Feldeffekttransistoren, die integrierten Kohlenstoffnanoröhrchen.:Bibliographische Beschreibung 3 Table of Contents 5 1 Introduction 7 2 Background 9 2.1 Structure of carbon nanotubes 9 2.2 Raman spectroscopy basics 10 2.3 Raman spectroscopy on graphene 14 2.4 Raman spectroscopy on carbon nanotubes 16 2.4.1 First-order Raman bands 18 2.4.2 Second-order Raman bands 20 2.5 How to analyze Raman spectra of single-wall carbon nanotubes 21 2.5.1 Diameter and chirality identification 22 2.5.2 Defect characterization 23 2.5.3 Doping and its connection to defects 25 2.5.4 Other effects that can cause frequency shifts 27 2.6 Tip-enhanced Raman spectroscopy 27 2.6.1 TERS experimental requirements 30 2.6.2 Tip and the signal enhancement 30 2.6.3 Brief summary of TERS on single-wall carbon nanotubes 31 3 Materials and Methods 33 3.1 Raman spectroscopy 33 3.2 Ion beam irradiation 34 3.3 SWCNT samples 35 3.4 SWCNT thin film preparation by vacuum filtration 36 3.5 Field effect transistor fabrication and electrical characterization 37 3.6 Tip-enhanced Raman spectroscopy 39 3.6.1 Preparation of the TERS tips 39 3.6.2 Instrumentation 39 3.6.3 SWCNT sample preparation 40 4 Preparation of carbon nanotube thin films 41 4.1 Removal of SDS 42 4.2 Removal of the density gradient medium 43 4.3 Summary 44 5 Quantifying defects in single-wall carbon nanotubes 45 5.1 Parameters of the defect creation 46 5.2 Reference measurement on ion irradiated graphite 47 5.3 Qualitative description of SWCNT defect development 48 5.3.1 Quantitative analysis of the SWCNT defects 57 5.3.2 Summary 59 6 Raman spectroscopy applied to investigate carbon nanotube transistors 61 6.1 Effect of chemical and thermal cleaning of SWCNTs 61 6.2 Effect of temperature and doping on SWCNTs in a Field-effect transistor 65 6.2.1 Investigation of temperature effect 66 6.2.2 In operando CNT-FET Raman spectroscopy measurement 67 6.3 Summary 71 7 TERS on SWCNTs 73 7.1 Preparation of TERS tips 73 7.1.1 Corrosion protection for silver TERS probes 73 7.2 Spatial resolution 76 7.3 Raman spectra of an individual nanotube at the nanoscale 77 7.4 Summary 81 8 Conclusions 83 References 85 Acknowledgement 97 Selbstständigkeitserklärung 99 Lebenslauf 101 Publication list 103

Alla luce del recente allarmante tasso di esaurimento delle riserve di combustibili fossili e al contemporaneo drastico aumento dei livelli di CO2 nell'atmosfera, principale gas serra responsabile del riscaldamento globale e di cambiamenti climatici molto gravi, una delle priorità assolute nella ricerca a livello mondiale è quella di sfruttare il più possibile le fonti di energia rinnovabile. Una possibilità molto interessante è quella di realizzare un processo di riduzione della CO2 a combustibili liquidi che sfrutti energie rinnovabili, quale quella solare, mediante dispositivi più comunemente noti come celle fotosintetiche artificiali o foglie artificiali o celle foto-elettro-catalitiche (PEC). L'obiettivo principale di questo lavoro, è stato pertanto quello di condurre uno studio approfondito su due diversi sistemi elettrocatalitici di riduzione della CO2 a prodotti liquidi con un più alto valore aggiunto, uno operante in fase gassosa (cioè in assenza di elettrolita al catodo) e uno operante in fase liquida. In particolare, è stata progettata e utilizzata nel processo di conversione della CO2, un’innovativa cella in fase liquida operante su scala di laboratorio, sulla falsariga della cella in fase gas precedentemente sviluppata all’Università di Messina. Il lavoro è stato svolto principalmente presso il laboratorio CASPE/INSTM dell’Università degli Studi di Messina (Dipartimento di Ingegneria Elettronica, Chimica e Ingegneria Industriale). Un periodo di sei mesi è stato svolto invece, nel corso del secondo anno di dottorato, presso l’École supérieure de chimie, physique, électronique de Lyon (CPE Lyon). In tale periodo sono stati sintetizzati, mediante innovative tecniche di sintesi organometallica, materiali compositi da utilizzare come elettrocatalizzatori nel processo di riduzione della CO2. Sono state effettuate molteplici prove sperimentali utilizzando svariate tipologie di catalizzatori, sia in fase gas che in fase liquida, al fine di indagare la differente selettività, produttività e varietà di prodotti ottenuti. Il processo in fase liquida è infatti quello maggiormente studiato in letteratura, ma esistono alcune problematiche che devono essere superate per consentire un successivo semplice scale up. quali ad esempio, la scarsa solubilità della CO2 e la tipologia di prodotti ottenuti (principalmente acido formico). Lo scopo principale di questo lavoro è stato quello di preparare nuovi materiali a base di carboni dopati con metalli, catalizzatori questi molto diversi da quelli comunemente utilizzati nel processo di riduzione della CO2 (generalmente metalli in bulk), e di testarli sia in fase gas (per sfruttare i vantaggi di questa condizione, quali ad esempio facile recupero dei prodotti e alta qualità dei prodotti stessi) sia in fase liquida (per avere un miglior confronto con i dati ampiamente presenti in letteratura). Per gli studi sulla riduzione elettrocatalitica della CO2 nella cella operante in fase gassosa, sono stati preparati una serie di elettrodi (basati su nano particelle –NP- di Cu, Fe, Pt e Cu/Fe depositate su nanotubi di carbonio o carbon black e successivamente poste all'interfaccia tra una membrana di Nafion e uno strato a diffusione di gas –GDL-). I risultati ottenuti sono stati molto promettenti, sia in termini di tipologia di prodotti formati che di produttività. In fase gas (senza elettrolita) è stata osservata la formazione di prodotti ≥C1 quali etanolo, acetone e isopropanolo, in particolare utilizzando il Fe (seguito dal Pt), evidenziando che anche metalli non nobili possono essere usati in maniera efficiente in questo processo. Per migliorare la produttività nella reazione di riduzione della CO2, sono stati preparati elettrodi differenti, basati su coating con sostituti zeolitici imidazolici (SIM-1) tipo MOF. In particolare, i catalizzatori testati sono stati MOF modificati con Fe-CNT, Pt-CNT, e CuFe-CNT. E’ stato osservato un cambiamento significativo in termini di produttività e anche di selettività verso i prodotti finali. Nel dettaglio, in particolare per il catalizzatore a base di MOF modificato con Pt, è stato osservato un aumento nei prodotti carboniosi e anche una selettività più alta verso prodotti con un più elevato numero di atomi di C. Per quanto riguarda lo studio del processo di riduzione elettrocatalitica della CO2 utilizzando la cella operante in fase liquida, sono state preparate tipologie di elettrodi simili ai precedenti. Inizialmente infatti, sono stati studiati elettrodi a base di nanoparticelle metalliche (Cu, Fe, Pt, Ru, Co) depositate su nanotubi di carbonio o carbon black. L'ordine relativo della produttività nella riduzione elettrocatalitica della CO2 in questa serie di elettrodi, è però risultato essere diverso rispetto alla fase gassosa, indicando quindi un differente percorso di reazione. In termini di produttività totale, gli elettrodi a base di Pt hanno consentito di ottenere le migliori performance, seguiti da Ru e Cu, mentre il Fe ha dato risultati peggiori. Sulla base dei risultati sperimentali ottenuti, è stato inoltre ipotizzato un possibile meccanismo di reazione. Successivamente, per cercare di migliorare ulteriormente le prestazioni nel processo di riduzione della CO2 in fase liquida, è stato effettuato uno studio approfondito, volto ad indagare la dipendenza di tale processo dalle dimensioni delle nanoparticelle metalliche. A tale scopo sono stati utilizzati elettrodi a base di nanoparticelle metalliche (Ru, Fe, Pt e Cu) su nanotubi di carbonio (CNT) depositati su GDL. Sono state sintetizzate nanoparticelle metalliche di diverse dimensioni utilizzando molteplici tecniche di sintesi: (i) impregnazione che ha consentito di ottenere NP di dimensioni comprese tra 10-50 nm; (ii) sintesi organometallica che ha consentito di ottenere NP uniformi e ultrafine con dimensioni comprese tra 1-5 nm. (ad esempio sono state sintetizzate NP di Fe di 1-3 P nm) (iii) sintesi mediante nanowires che ha consentito di ottenere NP di rame ultrafine con dimensioni comprese tra 2-3,8 nm. In particolare, la novità dell’approccio mediante nanowires sta nella possibilità di ottenere particelle di dimensioni molto piccole sintetizzando inizialmente i Cu NWs, mettendoli poi a contatto con il supporto carbonioso e facilitandone il suo trasferimento, ciò grazie alle forze intermolecolari di attrazione dei gruppi funzionali presenti sui CNT parzialmente ossidati. Inoltre, a differenza della sintesi organometallica, tale approccio permette di condurre le reazioni in aria e non in atmosfera inerte. I valori di produttività ottenuti sono stati 5-30 volte più alti utilizzando nanoparticelle metalliche più piccole (ottenute via nanowires o mediante sintesi organometallica) rispetto alle nanoparticelle metalliche più grandi (ottenute per impregnazione). I risultati sperimentali indicano pertanto che le NP di dimensioni più piccole hanno un ruolo fondamentale nelle performance catalitiche. Inoltre, il carico di NP metalliche è stato significativamente ridotto dal 10% al 1-2% in peso consentendo di ottenere, per le NP più piccole, una produttività equivalente o addirittura superiore rispetto alle nanoparticelle più grandi. In seguito, è stato effettuato anche uno studio sul possibile riutilizzo degli elettrodi di lavoro e sulla disattivazione per tempi di reazione più lunghi. E’ stata infine preparata una diversa tipologia di elettrodi a base di nano-foams su lastrine metalliche, al fine di ottenere un ulteriore miglioramento nel processo di riduzione elettrocatalitica della CO2. Le nano-foams o dendriti, sono state preparate mediante la tecnica di deposizione elettrochimica ed è stato effettuato uno studio preliminare di ottimizzazione, al fine di determinare le condizioni di sintesi più adatte. In aggiunta, è stato eseguito uno studio specifico per ottimizzare il valore di Voltaggio da utilizzare nelle prove catalitiche, mediante sia test di voltammetria ciclica che test completi di riduzione della CO2. Sono stati testati nano-foams a base di Cu e Fe depositati su fogli di Cu Fe, Al, di Inconel e su una griglia di Al. L’aumento nella produttività usando queste tipologie di elettrodi, è stata nell’ordine di 2-10 volte rispetto alla massima produttività ottenuta utilizzando NP metalliche su materiali carboniosi. Svariate tecniche analitiche sono state poi utilizzate per caratterizzare in modo approfondito i materiali preparati tra cui, microscopia elettronica a trasmissione (TEM), microscopia elettronica a scansione (SEM), spettroscopia ad assorbimento atomico (AAS), diffrazione a raggi X (XRD), spettroscopia fotoelettronica a raggi X (XPS), determinazione dell’area superficiale mediante metodo Brunauer-Emmett-Teller (BET). La determinazione dei prodotti di reazione è stata effettuata invece mediante cromatografia ionica (IC), gas cromatografia con rivelatore a spettrometria di massa (GC-MS), gas cromatografia (GC) con rivelatore a termo conducibilità (TCD).
In view of the recent alarming rate of depletion of fossil fuel reserves and the drastic rise in the CO2 levels in the atmosphere leading to global warming and severe climate changes, tapping into all kinds of renewable energy sources has been among the top priorities in the research fields across the globe. One of the many such pathways is CO2 reduction to fuels using renewable energies, more commonly referred as artificial photosynthetic cells or artificial leaves or photo-electro-catalytic (PEC) cells. The key objective of the present PhD work was to conduct in-depth studies on two different electro-catalytic CO2 reduction systems: electrolyte-less cell (gas phase) and electrolytic cell (liquid phase). In particular, a novel lab scale liquid phase cell, on the similar lines of the previously realized gas phase cell at the University of Messina, was developed and used to convert electro-catalytically CO2 to more value-added products. The work was carried out at the Laboratory CASPE/INSTM of the University of Messina (Department of Electronic Engineering, Industrial Chemistry and Engineering). During the second year, a six-month period was spent at the École supérieure de chimie, physique, électronique de Lyon (CPE Lyon), where organometallic routes were explored for the synthesis of novel composite materials to be used as electrocatalysts in the CO2 reduction process. Experimental tests were carried out on various types of catalysts in both the gas and liquid phase cells to understand the different selectivity, productivity and the reaction products obtained. Liquid phase, in fact, has been the most studied process in literature, but some issues mainly related to CO2 solubility and types of products formed (i.e. mainly formic acid), have never be allowed to pass the lab scale stage. The general aim of this PhD was to prepare novel metal doped nanocarbon substrates, which are very different with respect to the conventional metal bulk layers used as electrocatalysts in CO2 reduction, and test them both in gas phase (to take advantage of these conditions, i.e easy recovery and improved quality of the products) and in liquid phase (to have a better comparison with conditions typically adopted in literature). For the studies on the electro-catalytic reduction of CO2 in gas phase cell, a series of electrodes (based on Cu, Fe, Pt and Cu/Fe metal nanoparticles – NPs - deposited on carbon nanotubes – CNTs - or carbon black and then placed at the interface between a Nafion membrane and a gas diffusion-layer) were prepared. The results, evidencing the various types of products formed and their different productivities, are very promising. Under electrolyte-less conditions, the formation of ≥C1 products (such as ethanol, acetone and isopropanol) were observed, the highest being for Fe and closely followed by Pt, evidencing that also non-noble metals can be used as efficient catalysts under these conditions. To enhance the productivities of the CO2 reduction, a different set of electrodes were also prepared based on substituted Zeolitic Imidazolate (SIM-1) type MOF coatings during a stay at CPE Lyon and Institut de recherches sur la catalyse et l'environnement de Lyon (IRCELYON). Particularly, the catalysts tested were MOF-based Fe-CNTs, Pt-CNTs and Cu/Fe-CNTs. There was a significant change in the reaction products and in the selectivity towards the end-products. Particularly, especially for the MOF modified Pt based catalyst, there was an increase in the C-products and also a better selectivity towards higher C-products. Moving to the studies on the electro-catalytic reduction of CO2 in liquid phase cell, a similar set of electrodes were prepared. Initially, electrodes based on metal NPs of Cu, Fe, Pt, Ru and Co deposited on CNTs or carbon black were studied for their CO2 reduction capability. The relative order of productivity in CO2 electro-catalytic reduction in these series of electrodes was found to be different between the gas and liquid phase cells indicating the different reaction pathways. For liquid phase conditions, in terms of net C-products, catalytic electrodes based on Pt topped the class, closely followed by Ru and Cu, while Fe got the lowest position. The probable underlying reaction mechanism was also provided. In order to improve further the performances of the CO2 reduction in liquid phase conditions, a metal NPs size dependant study on the electro-catalytic reduction of CO2 to fuels was carried out. This study was performed using electrodes based on metal NPs of Ru, Fe, Pt and Cu loaded on CNTs and then transferred on a gas diffusion layers (GDL). Varied sized metal NPs have been synthesized using different techniques: (i) impregnation route to achieve NPs in the size range of 10-50 nm; (ii) organometallic approach to synthesize uniform and ultrafine NPs in the size range of 1-5 nm (i.e., Fe NPs were synthesized through a novel synthesis route to attain 13 nm NPs);(iii) Nanowire (NW) top-down approach to obtain ultrafine copper metal NPs in the size range of 2-3.8 nm. Particularly, the novelty of nanowire approach is the ability to obtain very small metal NPs starting from the synthesis of Cu NWs and then transferring the Cu onto the carbon surface, taking advantage of the different inter-forces of between Cu NWs and the functional groups present on the partially oxidized CNT surface. Furthermore, unlike the case of organo-metallic approach, this approach allows a preparation under air avoiding the use of potentially demanding inert atmospheric conditions. The enhancements in the fuel productivity were found to be 5-30 times higher for the smaller metal NPs obtained via organo-metallic route or nanowire route as compared to the larger metal NPs obtained via impregnation route. The results signify that the smaller sized metal NPs loading on the CNTs have a prevailing role in the catalytic performance and the selectivity towards different products. Moreover, the percentage of metal NPs loading was significantly reduced from 10 to 1-2 wt. % producing higher or equivalent fuels for small NPs as compared to the larger NPs. The reusability of the working electrodes and long reaction times (until 24 hours) were also probed. A different set of electrodes based on nano-foams on metal foils, were also investigated to achieve further improvements in the electro-reduction of CO2 to fuels. These nano-foams or dendrites were prepared by electrochemical deposition technique. Optimization studies on the deposition of these foams were performed initially to fix the set of preparation conditions. Moreover, voltage optimization study was performed using cyclic voltammetry and full CO2 reduction tests to find the optimum voltage for the process. The nano-foam electrodes tested include Cu and Fe foams on Cu foil, Fe foil, Al foil, Inconel foil and Al grid/mesh. The enhancements in the fuel productivity for various foams were in the range of 2-10 times greater as compared to the highest net fuel productivity achieved using metal NPs doped carbon catalytic electrodes, from all the previous studies. Various characterizations and analysis tools were used to analyse the catalysts qualitatively and quantitatively, which include Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Atomic Absorption Spectroscopy (AAS), X-ray diffraction (XRD), X-ray Photo-electron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET). To determine the fuel productivities, Ion Chromatography (IC), Gas Chromatography-Mass Spectrometer (GC-MS), Gas Chromatography (GC) were used.
Compte tenu du récent taux alarmant d'épuisement des réserves de combustibles fossiles et de l'augmentation drastique des niveaux de CO2 dans l'atmosphère qui a conduit au réchauffement de la planète et à des changements climatiques sévères, l'exploitation de toutes sortes d'énergies renouvelables a été la Parmi les principales priorités de la recherche Champs à travers le monde. L'une des nombreuses voies de ce genre est la réduction du CO2 aux combustibles utilisant des énergies renouvelables, plus communément appelées cellules photosynthétiques artificielles ou feuilles artificielles ou cellules photoélectro-catalytiques (PEC). L'objectif principal de ce travail était de réaliser des études approfondies sur les différents systèmes de réduction électro-catalytique du CO2, à savoir les cellules sans électrolyte (phase gazeuse) et les cellules électrolytiques (phase liquide). Dans ce processus, nous avons conçu une nouvelle cellule en phase liquide à échelle de laboratoire sur les lignes similaires de la cellule de phase gazeuse de modèle précédemment modélisée. Des essais expérimentaux sur la réduction du CO2 ont été réalisés sur différents types de catalyseurs dans les deux cellules afin de comprendre la sélectivité, la productivité et les produits de réaction obtenus. L'obtention de résultats de test dans les deux cellules nous a permis d'effectuer une comparaison décente avec les résultats de réduction électro-catalytique de CO2 existants dans la littérature. Des essais expérimentaux ont été réalisés sur différents types de catalyseurs à la fois dans les cellules en phase gazeuse et en phase liquide pour comprendre la sélectivité, la productivité et les produits de réaction obtenus. La phase liquide, en fait, a été le processus le plus étudié dans la littérature, mais certaines questions liées principalement à la solubilité du CO2 et aux types de produits formés (c'est-à-dire principalement l'acide formique) n'ont jamais été autorisées à franchir le stade de l'échelle du laboratoire. L'objectif général de ce doctorat était de préparer de nouveaux substrats de nanocarbone dopés par des métaux, qui sont très différents par rapport aux couches en vrac métalliques conventionnelles utilisées comme électrocatalyseurs dans la réduction de CO2, et de les tester en phase gazeuse (pour profiter de ces conditions, Une récupération facile et une qualité améliorée des produits) et en phase liquide (pour une meilleure comparaison avec les conditions typiquement adoptées dans la littérature). Pour les études sur la réduction électro-catalytique du CO2 en phase gazeuse, une série d'électrodes (à base de nanoparticules de Cu, Fe, Pt et CuFe déposées sur des nanotubes de carbone ou de noir de carbone puis placées à l'interface entre une membrane Nafion et Une électrode à couche de diffusion de gaz). Les résultats démontrent le type divers de produits formés et leurs productivités. Dans des conditions sans électrolyte, la formation de produits ≥C1 tels que l'éthanol, l'acétone et l'isopropanol a été observée la plus élevée étant pour Fe et suivie de près par Pt. Pour améliorer les productivités de la réduction du CO2, un ensemble différent d'électrodes a été préparé sur la base de revêtements MOF de type imidazolate de type zéolitique substitué (SIM-1) lors d'un séjour au CPE Lyon et à l'Institut de recherches sur la catalyse et l'environnement de Lyon (IRCELYON). Les catalyseurs testés étaient Fe-CNT, Pt-CNT et CuFe-CNT basés sur MOF. Il y a eu un changement significatif dans les produits de réaction et aussi, la sélectivité vis-à-vis des produits finaux. Pour le catalyseur à base de Pt modifié, MOF, il y avait une augmentation des produits C et également une sélectivité différente tandis que pour le catalyseur à base de Fe, il y avait une légère diminution des produits C. En se reportant aux études sur la réduction électro-catalytique du CO2 dans une cellule en phase liquide, un ensemble similaire d'électrodes a été préparé afin d'obtenir une bonne comparaison des résultats dans les expériences en phase gazeuse. Initialement, des électrodes à base de nanoparticules métalliques (Cu, Fe, Pt, Ru, Co) déposées sur des nanotubes de carbone ou du noir de carbone ont été étudiées pour leur capacité de réduction du CO2. L'ordre relatif de productivité dans la réduction électrocatalytique de CO2 dans ces séries d'électrodes a été trouvé différent entre les cellules en phase gazeuse et en phase liquide indiquant les différentes voies de réaction. Pour les conditions de phase liquide, en termes de produits C nets, les électrodes catalytiques à base de Pt sont en tête de la catégorie, suivies de près par Ru et Cu, tandis que Fe a obtenu la position la plus basse. Le mécanisme réactionnel sous-jacent probable a également été fourni. Afin d'améliorer encore les performances de la réduction du CO2 dans les conditions de phase liquide, une étude de la nanoparticules métalliques (NPs) dépendant de la taille de la réduction électro-catalytique du CO2 aux combustibles a été réalisée. Ceci a été réalisé à l'aide d'électrodes à base de nanoparticules métalliques (Ru, Fe, Pt et Cu) chargées sur les nanotubes de carbone (CNT) transférés sur les couches de diffusion gazeuse (GDL). On a synthétisé des nanoparticules de métal de différentes tailles en utilisant différentes techniques de synthèse: (i) l'itinéraire d'imprégnation pour obtenir des NP dans la plage de tailles de 10 à 50 nm; (Ii) Approche organométallique pour synthétiser des NPs uniformes et ultrafines dans la plage de tailles de 1-5 nm. Fe ont été synthétisés par une nouvelle voie de synthèse et des conditions pour atteindre des NP de 1 à 3 nm. (Iii) Approche de haut en bas de Nanowire pour obtenir des NP métalliques de cuivre ultrafin dans la plage de taille de 2-3,8 nm. En particulier, la nouveauté de l'aide de nanofils est la capacité à obtenir des particules de très petite taille d'abord la synthèse du Cu NFs, puis de les mettre en contact avec le support carboné et de faciliter son transfert, cela grâce à des forces d'attraction intermoléculaires des groupes fonctionnels présent sur le CNT partiellement oxydée. En outre, contrairement à la synthèse organométallique, cette approche permet d'effectuer les réactions dans l'air et non pas dans une atmosphère inerte. Les améliorations de la productivité du combustible ont été trouvées être au moins 5 à 30 fois plus élevées pour les NP métalliques de plus petite taille obtenus par voie organo-métallique ou par nanofil, par rapport aux NP métalliques plus grands obtenus par voie d'imprégnation. Les résultats indiquent que les NP métalliques de plus petite taille chargés sur les CNT jouent un rôle prédominant dans la performance catalytique et la sélectivité vis-à-vis de différents produits. En outre, le pourcentage de charge de NP métalliques a été réduit de façon significative de 10% à 1-2% en poids, produisant des carburants plus élevés ou équivalents pour de petites NP en comparaison avec les NP plus grandes. De plus, comme on a observé clairement la productivité en H2 qui a augmenté de nombreux facteurs pour les NP plus petits sur les plus grandes NP. La réutilisabilité des électrodes de travail et les longs temps de réaction ont également été sondés. Un ensemble différent d'électrodes à base de nano-mousses sur des feuilles métalliques a également été étudié afin d'obtenir des améliorations beaucoup plus importantes de l'électro-réduction de CO2 aux carburants. Ces nano-mousses ou dendrites ont été préparées par une technique de dépôt électrochimique. Des études d'optimisation sur le dépôt de ces mousses ont été effectuées initialement pour fixer l'ensemble des conditions de préparation. De plus, une étude d'optimisation de la tension a été réalisée en utilisant la voltamétrie cyclique et des tests de réduction de CO2 complets pour fixer une tension optimale pour les réactions. Les électrodes nano-mousses testées incluent (mousses Cu, Fe sur feuille Cu, feuille Fe, feuille Al, feuille Inconel et grille Al). Les améliorations de la productivité du combustible pour diverses mousses se situaient dans la plage de 2 à 10 fois par rapport à la productivité nette de combustible la plus élevée obtenue en utilisant des électrodes catalytiques en carbone dopé par des NP métalliques. Différentes caractérisations et outils d'analyse ont été utilisés pour analyser les catalyseurs qualitativement et quantitativement qui incluent la microscopie électronique à transmission (TEM), la microscopie électronique à balayage (SEM), la spectroscopie d'absorption atomique (AAS), la diffraction des rayons X (XRD) La spectroscopie électronique (XPS) et Brunauer-Emmett-Teller (BET) et pour déterminer les productivités des combustibles, chromatographie ionique (IC), chromatographie gazeuse-spectromètre de masse (GC-MS), chromatographie gazeuse.