In order to improve the purity of steel castings, the use of special reactive coatings on carbon-bonded ceramic foam filters was explored. Carbon nanotubes were dispersed in water by means of ultrasonic treatment, using xanthan gum to stabilize the nanotubes in suspension and control the rheological behavior. The coatings were applied by cold spraying and binding was achieved during heat treatment in reducing atmosphere, thanks to an artificial pitch added to the slurry. The coated filters were successfully immersed in molten steel for different times. The thickness of the first alumina layer generated at the interface was independent of the immersion time: concentration gradients through its thickness suggested that the formation of this structure is limited by diffusion. Investigation of the steel after solidification by means of ASPEX showed that the presence of the coating influenced the size as well as the chemical composition of the remaining inclusions. Nano-coated filters had the best filtration efficiency (up to 95% for alumina inclusions after 10 s), but longer tests resulted in worse performance. In addition, coatings based on calcium aluminates in combination with carbon showed an efficiency greater than 97% for steel samples taken directly from the melt.

In order to improve the purity of steel castings, the use of special reactive coatings on carbon-bonded ceramic foam filters was explored. Carbon nanotubes were dispersed in water by means of ultrasonic treatment, using xanthan gum to stabilize the nanotubes in suspension and control the rheological behavior. The coatings were applied by cold spraying and binding was achieved during heat treatment in reducing atmosphere, thanks to an artificial pitch added to the slurry. The coated filters were successfully immersed in molten steel for different times. The thickness of the first alumina layer generated at the interface was independent of the immersion time: concentration gradients through its thickness suggested that the formation of this structure is limited by diffusion. Investigation of the steel after solidification by means of ASPEX showed that the presence of the coating influenced the size as well as the chemical composition of the remaining inclusions. Nano-coated filters had the best filtration efficiency (up to 95% for alumina inclusions after 10 s), but longer tests resulted in worse performance. In addition, coatings based on calcium aluminates in combination with carbon showed an efficiency greater than 97% for steel samples taken directly from the melt.

Carbon nanotubes (CNTs) have attracted a significant attention in a wide variety of applications due to their excellent physical and chemical properties. Specifically, CNTs reinforced polymer nanocomposites have considerable potential for the realization of highly sensitive, flexible, stable and durable strain sensors. However, the performance of polymer/CNTs strain sensors is influenced by many factors. Especially, the homogeneity of the CNTs distribution within the polymer matrix and the adhesion of nanocomposite film to the polymer substrate play a decisive role. Additionally, the electrical and piezoresistive responses of polymer/CNTs nanocomposites, as well as their response under variable environmental conditions need to be considered. The main aim of this thesis is to develop polymer/CNTs nanocomposites for strain sensing applications. Thereby, the focus is on the development of suitable, cost-effective and simple preparation methods of polymer/CNTs-based strain sensitive nanocomposites and on the selection of suitable flexible substrate. However, during deposition, residual stress can be formed at the interface between the film and the substrate, which leads to thin film failures. Therefore, an analytical model is developed to predict the stress distribution in the film aiming to define the suitable processing conditions for low residual stress formations. Furthermore, specific surface treatments are proposed in order to enhance the adhesion between the substrate and the thin film, which are investigated by contact angle measurement (CAM), X-rays spectroscopy (XPS)and atomic force microscopy (AFM). Nanocomposites with up to 1 wt.% multi-walled carbon nanotubes (MWCNTs) were prepared using a simple direct mixing method. The process parameters, such as sonication time and curing time, have been determined based on several characterization techniques. Dispersions qualities were examined using morphological and topography characterizations including scanning electron microscopy (SEM) and AFM. Additionally, DC measurements were performed on the polymer/CNTs nanocomposites in order to optimize the process parameters depending on the electrical conductivity and piezoresistivity of the nanocomposite. The impact of surface treatment on the strain sensing behavior was evaluated. Furthermore, electrical and piezoresistive responses under humidity and temperature effects were investigated. Analytical investigations show that the residual stresses can be minimized by using low deposition temperatures and by increasing the film thickness. Comparison of surface treatment techniques demonstrates that oxygen plasma cleaning improves adhesion at the interface by enlarging the surface area and enhancing the surface wettability and the surface polarity due to the introduction of functional groups. Morphological characterizations show the good homogeneity of MWCNTs and depict the importance of optimization of sonication time for the uniform filler distribution. Furthermore, AFM analysis show that the surface roughness is reduced as sonication time is increased due to the debundling of CNTs agglomeration. However, excessive sonication time can lead to higher roughness caused by breaking of CNTs, which get thereby the tendency to re-agglomerate. A low percolation threshold was achieved at a CNTs concentration of 0.3 wt.% which is significantly lower than the CNT concentrations reported in literature and demonstrating the quality of dispersion process adopted. Higher sensitivity is achieved at this CNTs concentration with approximately linear piezoresistive behavior of around R 2 = 0.9904. The novel strain sensitive nanocomposites show good stability at ambient conditions and good durability under mechanical cyclic test. In addition, it is found that the sensing behavior depends greatly on the surface roughness. A high stability and linearity with good sensitivity were observed for the sensor having low surface roughness. The temperature and humidity dependency of the composite is affected by the environmental changes. Therefore, an encapsulation of the film is required to minimize moisture absorption in addition to get better sensor recovery under mechanical load comparing to non-encapsulated film. / Kohlenstoff-Nanoröhrchen (CNTs) genießen aufgrund ihrer hervorragenden physikalischen und chemischen Eigenschaften in einer Vielzahl von Anwendungen eine große Aufmerksamkeit. Insbesondere CNT-verstärkte polymere Nanokomposite haben ein erhebliches Potenzial für die Realisierung hochempfindlicher, flexibler, stabiler und langlebiger Dehnungssensoren. Die Eigenschaften von Polymer/CNT-Dehnungssensoren werden von vielen Faktoren beeinflusst. Insbesondere die Homogenität der CNT-Verteilung innerhalb der Polymermatrix und die Haftung des Nanokompositfilms auf dem Polymersubstrat spielen eine entscheidende Rolle. Darüber hinaus müssen die elektrischen und piezoresistiven Eigenschaften von Polymer/CNTs-Nanokompositen sowie deren Reaktion auf variable Umgebungsbedingungen berücksichtigt werden. Das Hauptziel dieser Arbeit ist die Entwicklung von Polymer/CNT-Nanokompositen für die Anwendung als Dehnungsmessstreifen. Der Fokus liegt auf der Entwicklung geeigneter, kostengünstiger und einfacher Präparationsmethoden von Polymer/CNT-basierten dehnungsempfindlichen Nanokompositen und deren Realisierung auf geeigneten flexiblen Substraten. Während der Abscheidung kann an der Grenzfläche zwischen Film und Substrat Eigenspannung entstehen, die zu Dünnschichtfehlern führt. Daher wird ein analytisches Modell zur Vorhersage der Spannungsverteilung im Film entwickelt, um die geeigneten Verarbeitungsbedingungen für geringe Eigenspannungsformationen zu definieren. Darüber hinaus werden spezifische Oberflächenbehandlungen vorgeschlagen, um die Haftung zwischen dem Substrat und dem Dünnfilm zu verbessern, die durch Kontaktwinkelmessung (CAM), Röntgenspektroskopie und Rasterkraftmikroskopie (AFM) untersucht werden. Nanokompositen mit bis zu 1 wt.% mehrwandigen Kohlenstoff-Nanoröhren (MWCNTs) wurden mit einem einfachen Direktmischverfahren hergestellt. Die Prozessparameter, wie Ultraschallzeit und Aushärtezeit, wurden auf der Grundlage verschiedener Charakterisierungstechniken bestimmt. Die Dispersionsqualitäten wurden mittels morphologischer und topographischer Charakterisierungen einschließlich Rasterelektronenmikroskopie (REM) und AFM untersucht. Zusätzlich wurden DC-Messungen an den Polymer/CNT-Nanokompositen durchgeführt, um die Prozessparameter in Abhängigkeit von der elektrischen Leitfähigkeit und der Piezoresistivität des Nanokomposits zu optimieren. Der Einfluss der Oberflächenbehandlung auf das Verhalten des Dehnungssensors wurde bewertet. Darüber hinaus wurden elektrische und piezoresistive Reaktionen unter Feuchtigkeits- und Temperatureinflüssen untersucht. Analytische Untersuchungen zeigen, dass die Eigenspannungen durch niedrige Depositionstemperaturen und eine Erhöhung der Schichtdicke minimiert werden können. Der Vergleich von Oberflächenbehandlungstechniken zeigt, dass die Sauerstoff-Plasma-Reinigung die Haftung an der Grenzfläche verbessert, in dem sie die Oberfläche vergrößert und die Benetzbarkeit der Oberfläche sowie die Oberflächenpolarität durch die Einführung von Funktionsgruppen verbessert. Morphologische Charakterisierungen zeigen die gute Homogenität vom Epoxid /MWCNTs Nanokompositen und die Bedeutung der Optimierung der Ultraschallzeit für die gleichmäßige Füllstoffverteilung. Darüber hinaus zeigt die AFM Analyse, dass die Oberflächenrauhigkeit durch die Entbündelung der CNT-Agglomerate für eine längere Ultraschallzeit reduziert wird. Eine übermäßige Ultraschallzeit kann jedoch zu einer höheren Rauigkeit durch Brüche von CNTs führen, die dadurch zu einer erhöhten Reagglomerationsneigung führen. Ein niedriger Perkolationsschwellenwert wurde bei einer CNT-Konzentration von 0.3 wt.% erreicht, welches deutlich niedriger als die in der Literatur berichteten CNT-Konzentrationen ist. Dies belegt die hohe Qualität des vorgeschlagenen Dispersionsprozesses. Eine höhere Empfindlichkeit wird bei dieser CNT-Konzentration mit einem annähernd linearen piezoresistiven Verhalten von etwa R 2 = 0.9904 erreicht. Die neuartigen spannungsempfindlichen Nanokompositen weisen eine gute Stabilität der Umgebungsbedingungen und eine gute Haltbarkeit im mechanischen Zyklustest auf. Darüber hinaus wird festgestellt, dass das Abtastverhalten stark von der Oberflächenrauheit abhängt. Eine hohe Stabilität und Linearität bei guter Empfindlichkeit wurde für den Sensor mit geringer Oberflächenrauigkeit beobachtet. Das Verhalten des Sensors wird durch Umweltveränderungen aufgrund von Temperatur und Luftfeuchtigkeit beeinflusst. Daher ist eine Verkapselung des Films erforderlich, um die Feuchtigkeitsaufnahme zu minimieren. Die realisierte Verkapselung hat zusätzliche Vorteile in Bezug auf die Sensor Rückgewinnung unter mechanischer Belastung im Vergleich zu nicht gekapseltem Film gezeigt.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: In this research the possible utilization of carbon nanomaterials in gas sensing applications are investigated. These materials include the 2-dimensional honeycomb-lattice carbon structure called graphene, and the 1-dimensional structures referred to as carbon nanotubes (CNTs). The extraordinary properties and unique morphology of these nanomaterials, make them excellent candidates for sensory applications. This research thus entails the investigation and development of gas sensors with these carbon nanomaterials. This includes the synthesis of CNTs via a chemical vapour deposition (CVD) technique and the fabrication of resistive thin film sensors with the various materials. The functionalization of carbon nanomaterials is also explored, which delivers promising results for sensing gases at room temperature, especially acetylene (C2H2). Furthermore, a unique method is developed to fabricate ultra thin aluminium microstructures. These metallic electrodes are found to be ideal for nanomaterial integration. An experiment is performed to manufacture an integrated sensor with MWCNTs and following the results, a refinement of the procedure and the investigation of FET-based devices are recommended. The results obtained during this work, indicate that engineered carbon nanostructures, such as CNTs and graphene, can potentially be applied in future sensing technologies. / AFRIKAANSE OPSOMMING: Hierdie navorsing ondersoek die moontlike toepassing van koolstof nano-materiale as gas-sensor tegnologie. Hierdie materiale sluit die 2-dimensionele koolstof struktuur, grafeen, asook die sogenaamde 1-dimensionele koolstof nano-buise in. Die buitengewone eienskappe en unieke morfologie van hierdie nano-materiale, maak hul uitstekende kandidate vir sensor toepassings. Hierdie navorsing ondersoek dus die ontwikkeling van gas-sensors met koolstof nano-materiale, insluitend die sintese van koolstof nano-buise deur middel van ’n chemiese damp-neerslag proses, asook die fabrikasie van resistiewe dun film sensors. Die funksionalisering van koolstof nano-materiale is ook ondersoek en belowende resultate is opgelewer met betrekking tot die deteksie van gasse by kamertemperatuur, veral vir asetileen (C2H2) gas. Verder is ’n unieke metode ontwikkel om ultra dun aluminium mikrostrukture te vervaardig en hierdie metaal elektrodes word as ideaal beskou vir die integrasie van nano-materiale. ’n Eksperiment is uitgevoer om ’n geïntegreerde sensor te vervaardig met multi-wand koolstof nano-buise, waarvan die resultate aandui dat die proses verfyn moet word en dat die moontlike toepassing van veld-effek-transistor toestelle ondersoek moet word. Die resultate wat opgelewer is gedurende hierdie navorsing dui daarop dat ontwikkelde nanostrukture, soos koolstof nano-buise en grafeen, as toekomstige sensor tegnologie geïmplementeer kan word.

A small-scale model of a CVD reactor was built. Axial and radial of major species concentrations and temperature profiles were obtained with a micro gas chromatograph and a fine thermocouple. Those temperature and species concentrations revealed detailed thermal and chemical structures of the CVD reactor. The concentrations of argon plus hydrogen, methane, and C2Hx (C2H2 + C2H4 + C2H6) resulting from xylene decomposition were measured along the CVD at different temperatures. Ferrocene was added to xylene to investigate the effect of a catalyst on composition profiles. The results with ferrocene indicated an increase in CH4 and C2Hx concentrations. At 1000 C and above, the increase of C2Hx concentration is higher than that for CH4. The effect of ferrocene was very minor on the concentration of the gases. Finally composition and temperature profiles were measured and plotted for the radial direction at X=75 cm and T=1200 C. The overall rate constant for the gas-phase reaction was calculated based on the measured species concentration data using the Benson and Shaw reaction mechanism. Our study showed that the Benson and Shaw mechanism could be used in the temperature range lower than 800 C. Also the effect of hydrogen in the syntheses of CNTs, in the CVD reactor using xylene and ferrocene, was studied. Both single-step and two-step methods were applied. In the single-step method, the ferrocene was dissolved in the xylene. In the two step-method the catalyst preparation step was performed first; ferrocene powder was placed in the preheater for a certain period of time and carried by a mixture of argon and hydrogen at fixed concentration to get catalyst nanoparticles deposited on the reactor wall. Xylene then was injected to the reactor. To study the effect of hydrogen, the synthesized materials were observed by SEM and TEM. The results showed that the presence of hydrogen is essential for CNTs to be synthesized by the CVD method, and also the concentration of hydrogen in the reactor has a great effect on the quality of CNTs. The yield of CNTs in the two-step method was slightly higher than that in the one-step method.

Thin film material properties and measurement characterisation techniques are crucial for the development of micro-electromechanical systems (MEMS) devices. Furthermore, as the technology scales down from microtechnology towards nanotechnology, nanoscale materials such as carbon nanotubes (CNTs) are required in electronic devices to overcome the limitations encountered by conventional materials at the nanoscale. The integration of CNTs into micro-electronics and material applications is expected to provide a wide range of new applications. The work presented in this thesis has contributed to the development of thin film material characterisation through research on the thermal conductivity measurement and the control of the residual stress of thin film materials used commonly in MEMS devices. In addition, the use of CNTs in micro-electronics and as filler reinforcement in composite materials applications have been investigated, leading to low resistivity CNTs interconnects and CNTs-Polyimide (PI) composites based resistive humidity sensors. In the first part of this thesis, the thermal conductivity of conductive thin films as well as the control of the residual stress arising from fabrication process in PI micro-cantilevers have been studied. A MEMS device has been developed for the thermal conductivity characterisation of conductive thin films showing good agreement with thermal conductivity of bulk material. Low energy Ar+ ion bombardment in a plasma has been used to control the residual stress present in PI cantilevers. Appropriate ion energy and exposure time have led to stress relaxation of the beams resulting in a straight PI cantilever beam. In the second part of this thesis, low resistivity CNTs interconnects have been developed using both dielectrophoresis (DEP) and Focused Ion Beam (FIB) techniques. An investigation of the effects of CNT concentration, applied voltage and frequency on the CNTs alignment between Al and Ti electrodes has resulted in the lowering of the CNTs’ resistance. The deposition of Pt contact using FIB at the CNTs-metal electrodes interface has been found to decrease the high contact resistances of the devices by four and two orders of magnitude for Al and Ti electrodes respectively. The last part of this thesis focuses on the preparation of CNTs-PI composite materials, its characterisation and its application as resistive humidity sensor. The integration of CNTs inside the PI matrix has resulted in enhancing significantly the electrical and mechanical properties of the composites. In particular, a DEP technique employed to induce CNTs alignment inside the PI matrix during curing has been attributed to play an important role in improving the composite properties and lowering the percolation threshold. In addition, the fabrication and testing of CNTs-PI resistive humidity sensors have been carried out. The sensing performance of the devices have shown to be dependent highly on the CNT concentration. Finally, the alignment of CNTs by DEP has improved the sensing properties of CNTs-PI humidity sensors and confirmed that the change of resistance in response to humidity is governed by the change of the CNTs’ resistances due to charge transfer from the water molecules to the CNTs.

Recently there have been considerable interests in nanometerial study. In this work, we have used carbon nanotubes (CNTs) and polypyrrole (PPy) conducting polymers (CPs) as models to make a nanotube and conducting polymer composite material. Under electro-oxidation condition, the PPy/CNT films can be grown on conventional substrates such as a glassy carbon electrode in aqueous and non-aqueous media. These nano-conjugated materials are based on the doping of CNTs particles into conducting polymer network while oxidatively polymerizing. CNTs serve as dopants and solely supporting electrolytes in the preparation. The CP/CNT new composite materials have showed promise not only in a potential environmental remedy such as conversion of highly toxic Cr(VI) into less harmful Cr(III), but also in electrocatalysis of the quinone/hydroquinone redox reaction. Voltammetry, bulk electrolysis with coulometry, AC impedance, and EQCM techniques have been used to elucidate the preparation, ion transport, and intermolecular interaction processes within these composites.

The search for new materials for hydrogen storage is important for the development of future hydrogen energy applications. In this Thesis, it is shown that new materials with interesting properties can be synthesized by the reaction of hydrogen with various nanocarbon precursors. The thesis consists of two parts. The first part is devoted to studies of hydrogen storage in some metal-organic frameworks (MOFs) and nanostructured carbon materials, while the second part describes synthesis of new materials by the reaction of hydrogen gas with various carbon materials (i.e. fullerene C60, single-walled carbon nanotubes (SWCNTs), and fullerene C60 encapsulated inside SWCNTs (C60@SWCNTs)). Hydrogen adsorption was measured for a set of Zn- and Co-based MOFs at near ambient temperatures. MOFs synthesized using different metal clusters and organic connecting ligands allowed to study effects of different surface area, pore volume, and pore shapes on hydrogen storage parameters. Hydrogen adsorption values in the studied MOFs correlated well with surface area and pore volume but did not exceed 0,75wt.%. Therefore, new methods to improve the hydrogen storage capacity in MOFs were investigated. The addition of metal catalysts was previously reported to improve significantly hydrogen storage in MOFs. In this thesis the effect of Pt catalyst addition on hydrogen adsorption in MOF-5 was not confirmed. Contrary to previous reports, hydrogen adsorption in MOF-5 mixed/modified with Pt catalysts had fast kinetics, correlated well with surface area, and was on the same level as for unmodified MOF-5. New nanostructured carbon materials were synthesized by the reaction between fullerene C60 and coronene/anthracene. Despite negligible surface area these materials adsorbed up to 0,45wt.% of hydrogen at ambient temperatures. The reaction of fullerene C60 with hydrogen gas was studied at elevated temperatures and hydrogen pressures. In situ gravimetric monitoring of the reaction was performed in a broad temperature interval with/without addition of metal catalysts (i.e. Pt and Ni). The reaction resulted in synthesis of hydrogenated fullerenes C60Hx (with x≤56) followed by fullerene cage fragmentation and collapse upon prolonged duration of hydrogen treatment. Possible mechanisms of C60 hydrogenation and fragmentation were discussed. It is demonstrated that reaction of SWCNTs with hydrogen gas at elevated temperatures and hydrogen pressures can be used for nanotube opening, purification from amorphous carbon, side-wall hydrogenation, and partial unzipping of SWCNTs. Some graphene nanoribbons (GNRs) were synthesized as the result of SWCNTs unzipping. A surprising ability of hydrogen to penetrate inside SWNTs and to react with encapsulated fullerene C60 was demonstrated. / Sökandet efter nya material för vätelagring är viktigt för utveckling av framtida väteenergitillämpningar. I denna avhandling visas att nya material med intressanta egenskaper kan syntetiseras genom reaktion av väte med olika nanokolprekursorer. Avhandlingen består av två delar. Den första delen ägnas åt studier av vätelagring i vissa metall-organiska fackverk (så kallade MOFs) och nanostrukturerade kolmaterial medan den andra delen beskriver syntes av nya material genom reaktion av vätgas med olika kolmaterial (dvs. fulleren C60, enkelväggiga kolnanorör (SWCNTs) och fulleren C60 kapslat i SWCNTs (C60 @ SWCNTs)). Väteadsorptionen mättes för ett antal Zn- och Co-baserade MOFs vid rumstemperatur. MOFs syntetiserades med hjälp av olika metallkluster och organiska ligander för att studera effekterna av olika yta, porvolym och porformer på vätelagringsparametrarna. Väteadsorptionsvärden i de studerade MOFs korrelerade väl med yta och porvolym, men översteg inte 0,75wt.%. Därför undersöktes nya metoder för att förbättra kapaciteten för vätelagring i MOFs. Tillsättning av metallkatalysatorer har tidigare rapporterats avsevärt förbättra vätelagring i MOFs. I denna avhandling kunde effekten av en tillsats av Pt-katalysator på väteadsorption i MOF-5 inte bekräftas. I motsats till tidigare rapporter hade väteadsorption i MOF-5 blandad/modifierad med Pt-katalysatorer snabb kinetik och korrelerade väl med arean, men var på samma nivå som för omodifierad MOF-5. Nya nanostrukturerade kolmaterial syntetiserades genom reaktion mellan fulleren C60 och coronene/antracene. Trots försumbar yta adsorberade dessa material upp till 0,45wt.% väte vid rumstemperatur. Reaktionen av fulleren C60 med vätgas studerades vid förhöjda temperaturer och vätetryck. In situ gravimetrisk övervakning av reaktionen utfördes i ett brett temperaturintervall med/utan tillsats av metallkatalysatorer (dvs. Pt och Ni). Reaktionen resulterade i syntes av hydrogenerade fullerener C60Hx (med x≤56) följt av fragmentering och kollaps av fullerenstrukturen vid förlängd varaktighet av vätebehandlingen. Möjliga mekanismer för hydrering och fragmentering av C60 diskuteras. Det har visats att reaktionen mellan SWCNTs och vätgas vid förhöjda temperaturer och vätetryck kan användas för öppning av nanorör, borttagning av amorft kol, funktionalisering av sidoväggar och partiell "blixtlåsöppning" av SWCNTs. Reaktionen kan också syntetisera grafen-nanoband (GNRs) som en följd av att SWCNTs öppnas på längden. En överraskande stor förmåga för väte att tränga in i SWNT och där reagera med inkapslade fullerenmolekyler C60 demonstrerades.

Carbon nanotubes show a wide range of transport behavior that varies from ballistic to hopping regime, depending on the nature of disorder in the system. Minute variations in disorder can lead from weak to strong localization, and this yields complex and intriguing features in the analysis of transport data. This dissertation reports an experimental study of charge transport in optically transparent single-wall carbon nanotube (SWNT) networks and field-effect devices. The SWNT network comprises randomly aligned (bundles of) tubes that have both high optical transparency in visible, near-infrared (IR) wavelength range and high electrical conductivity. Various aspects of charge transport in this material including magnetotransport, high electric-field transport and gate induced field-effect are investigated and presented within a consistent framework. The temperature dependence of resistance suggests hopping transport in the network. Since strong localization is observed for the disordered network, the disorder is further characterized by a magnetotransport study and a pulsed electric-field dependence study down to low temperatures (1.3 K). The magnetoresistance (MR) has contributions from two quantum effects -a forward interference mechanism leading to a negative MR and a wavefunction shrinkage mechanism leading to positive MR. The temperature dependence of the coefficient of this negative MR is shown to follow inverse power-law dependence, in accordance with theoretical predictions. The intrinsic parameters obtained from this analysis suggest a transverse localization of charge on the bundle boundaries. The electric-field dependence, measured to high fields, follows the predictions of hopping transport in high electric-field regime. A scaling analysis indicates that electric-field and temperature play similar roles in the transport. The calculated dependence of ‘threshold electric-field’ is also suggestive of this competing process between phonons and electric-field. The applicability of the concept of ‘effective temperature’ is explored for this system; the electric-field induced suppression of MR is studied. The network resistance as well as the optical transparency of the network is modulated with gate voltage using an electrolyte gate dielectric. The gating can tune the absorptions associated with the van Hove singularities in the SWNT DOS and a time response study for this ‘smart window’ is done for the modulation. A novel technique is used to characterize organic and nanotube field-effect transistors and this allows estimation of device parameters such as transconductance and channel impedance. The ac impedance of the SWNT network is also investigated as a possible tool to probe network connectivity. To summarize, the role of disorder in charge transport is investigated for these novel transparent SWNT networks using magnetic-field, electric-field, temperature and field-effect dependent transport measurements.

This report details work toward the fabrication of a single-electron transistor created from a single-walled carbon nanotube (SWNT). Specifically discussed is a method for growing carbon nanotubes (CNTs) via carbon vapor deposition (CVD). The growth is catalyzed by a solution of 0.02g Fe(NO3)3·9H2O, 0.005g MoO2(acac)2, and 0.015g of alumina particles in 15mL methanol. SWNT diameter ranges from 0.6 to 3.0 nm. Also discussed is a method to control nanotube growth location by patterning samples with small islands of catalyst. A novel “maskless” photolithographic process is used to focus light from a lightweight commercial digital projector through a microscope. Catalyst islands created by this method are approximately 400 μm2 in area.