When materials approach the size of few nanometers, they show properties which are significantly different from their bulk counterpart. Such unique/improved properties make them potential candidate for several emerging applications. At the reduced dimension, controlling the shape of nanocrystals provides an effective way to tune several material properties. In this regard, wet chemical synthesis has been established as the ultimate route to synthesize nanocrystals at ultra-small dimensions with excellent control over the morphology. However, the use of surfactant poses a barrier into efficient realization of its application as it requires a clean interface for better performance. Exercise of available cleaning protocols to clean the surface often leads to coarsening of the nanoparticles due to their inherent high surface curvature. For anisotropic nanomaterials, rounding of the shape is an additional problem. Anchoring nanomaterials onto substrates provides an easy way to impart stability. In this thesis, ultrathin Au nanowires, that are inherently unstable, have been shown to grow over a wide variety of substrates by in-situ functionalization. Use of nanomaterials as device component holds promise into miniaturization of electronics. But device fabrication in such cases require manipulation of nanomaterials with enhanced control. Dielectrophoresis offers an easy way to assemble nanomaterials in between contact pads and hence evolved as a promising tool to fabricate device with a good level of precision. Herein, directed assembly of ultrathin Au nanowires by dielectrophoresis, has been shown as an efficient strategy to fabricate devices based on the wires. Combining more than one nanocrystal, to form a heterostructure, often has the advantage of synergism and/or multifunctionality. Therefore, synthesis of heterostructure is highly useful in enhancing and/or adding functionalities to nanomaterials. There are several routes available in literature for synthesis of heterostructures. Newer strategies are being evolved to further improve performance in an application specific way. In that regard, a good understanding of mechanism of formation is crucial to form the desired product with the required functionality. For example, Au due to high electron affinity has been known to undergo reduction rather than cation exchange with chalcogenides. In this thesis, it has been shown that the final product depends on the delicate balance of reaction conditions and the system under study using CdS-Au as the model system. In yet another case, PdO nanotubes have been shown to form, on reaction of PdCl2 with ZnO at higher starting ratio of the precursors. In-situ generation of HCl provides an effective handle for tuning of the product from the commonly expected hybrid to hollow. Graphene has evolved as a wonder material due to its wide range of practical applications. Its superior conductivity with high flexibility has made it an important material in the field of nanoelectronics. In this thesis, an interesting case of packed crumpled graphene has been shown to sense a wide variety of strain/pressure which has applications in day to day life. The study reported in the thesis is organized as follows: Chapter 1 presents a general introduction to nanomaterials followed by the review of the available strategies to synthesize various 1D nanomaterials. Subsequently, a section on the classification of hybrid followed by the different synthetic protocols adopted in literature to synthesize them, have been provided. A review on the available methodologies for directed assembly of nanomaterials has been presented. Chapter 2 provides a summary of the materials synthesized and the techniques used for characterization of the materials. A brief description of all the synthetic strategy adopted has been provided. The basic principle of all the characterization techniques used, has been explained. A section explaining the principle of dielectrophoresis has also been presented. Chapter 3 presents a general method to grow ultrathin Au nanowires over a variety of substrates with different nature, topography and rigidity/flexibility. Ultrathin nanowires of Au (~2 nm in diameter) are potentially useful for various catalytic, plasmonic and device applications. Extreme fragility on polar solvent cleaning was a limitation in realizing the applications. Direct growth onto substrate was an alternative but poor interfacial energy of Au with most commercial substrates lead to poor coverage. In this chapter, in-situ functionalization of the substrates have been shown to improve Au nucleation dramatically which lead to growth of dense, networked nanowires over large area. Catalysis and lithography-free device fabrication has been demonstrated. Using the same concept of functionalization, SiO2 coating of the nanowires have been shown. A comparative study of thermal stability of these ultrafine Au nanowires in the uncoated and coated form, has been presented. Chapter 4 demonstrates an ultrafast device fabrication strategy with Au nanowires using dielectrophoresis. While dense growth of Au nanowires is beneficial for some applications, it is not so for some others. For example, miniaturization of electronics require large number of devices in a small area. Therefore, there is a need for methods to manipulate nanowires so as to place them in the desired location for successful fabrication of device with them. In this chapter, dielectrophoresis has been used for assembling nanowires in between and at the sides of the contact pads. Alignment under different conditions lead to an understanding of the forces. Fabrication of a large number of devices in a single experiment has been demonstrated. Chapter 5 presents a simple route to synthesize CdS-Au2Sx hybrid as a result of cation-exchange predominantly. Au due to high electron affinity has been shown in literature to undergo reduction rather than cation exchange with CdS. In this chapter, it has been shown that cation exchange may be a dominant product. The competition between cation exchange and reduction in the case of CdS-Au system has been studied using EDS, XRD, XPS and TEM. Thermodynamic calculation along with kinetic analysis show that the process may depend on a delicate balance of reaction conditions and the system under study. The methodology adopted, is general and may be applied to other systems. Chapter 6 presents an one pot, ultrafast microwave route to synthesize PdO hollow/hybrid nanomaterials. The common strategy to synthesize hollow nanomaterials had been by nucleation of the shell material on the core and subsequent dissolution of the core. In this chapter, a one step method to synthesize hollow PdO nanotubes, using ZnO nanorods as sacrificial template, has been shown. By tuning the ratio of the PdCl2 (PdO precursor) to ZnO, ZnO-PdO hybrid could be obtained using the same method. The PdO nanotubes synthesized could be converted to Pd nanotubes by NaBH4 treatment. Study of thermal stability of the PdO nanotubes has been carried out. Chapter 7 demonstrates a simple strategy to sense a variety of strain/pressure with taped crumpled graphene. Detection of ultralow strain (10-3) with high gauge factor is challenging and poorly addressed in literature. Taped crumpled graphene has been shown to detect such low strain with high gauge factor (> 4000). An ultra-fast switching time of 20.4 ms has been documented in detection of dynamic strain of frequency 49 Hz. An excellent cyclic stability for >7000 cycles has been demonstrated. The same device could be used to detect gentle pressure pulses with consistency. Slight modification of the device configuration enabled detection of high pressure. Simplicity of the device fabrication allowed fabrication of the device onto stick labels which could be pasted on any surface, for instance, floor. Hard pressing, stamping with feet and hammering shocks do not alter the base resistance of the device, indicating that it is extremely robust. Sealed arrangement of the graphene allowed operation of the device under water in detection of water pressure. Presence of trapped air underneath the tape enabled detection of air pressure both below and above atmospheric pressure.

[pt] Os sistemas de administração controlada de medicamentos (drug delivery) permitem a introdução de uma substância terapêutica no organismo e melhoram sua eficácia e segurança, controlando a taxa, o tempo e o local de liberação, o que diminui os efeitos colaterais.Nesse trabalho nos dedicamos a estudar dois possíveis sistemas de administração de fármacos: lipossomos associados a surfactantes, já bastante utilizados em farmacologia, e nanobastões de ouro, cujas propriedades únicas têm sido avaliadas em aplicações biomédicas. Os lipossomos têm-se destacado devido a sua estabilidade e baixa toxicidade, os surfactantes são tensoativos muito usados tanto em farmacologia como para estabilizar soluções coloidais de nanopartículas. Já os nanobastões de ouro têm perspectivas promissoras para utilização em entrega de fármacos devido a suas propriedades óticas e biocompatibilidade. Estudamos, por meio de espectrofotometria de fluorescência e de absorção UV-visível, a associação entre esses sistemas e uma classe de fármacos denominada fluorquinolonas, que são antibióticos de amplo espectro bacteriano. A norfloxacina (NFX), pertencente à segunda geração de fluorquinolonas, foi escolhida para esse trabalho por ser naturalmente fluorescente, o que facilita a análise das interações sem a introdução de sondas extrínsecas ao sistema. Segundo a literatura, a associação da NFX com íons metálicos produz modificações nas propriedades desse fármaco, como solubilidade e biodisponibilidade. Essas mudanças têm sido avaliadas como uma possível solução ao problema de resistência bacteriana a antibióticos. Esse trabalho foi dividido em duas partes: na primeira, estudamos a formação dos complexos ternários de NFX com cobre-fenantrolina em presença de lipossomos associados a surfactantes que modificam a distribuição de carga elétrica superficial desses sistemas; na segunda parte estudamos a associação de NFX a nanobastões de ouro estabilizados por diferentes surfactantes. / [en] Drug delivery systems allow the introduction of a therapeutic substance into the body and improve its effectiveness and safety by controlling the rate, time and place of release, which reduces side effects. In this work, we study two possible drug delivery systems: liposomes associated with surfactants, which are already widely used in pharmacology, and gold nanorods, whose unique properties have been evaluated in biomedical applications. Liposomes have been remarkable because of their stability and low toxicity, and surfactants are widely used both in pharmacology and to stabilize colloidal solutions of nanoparticles. On the other hand, gold nanorods have promising perspectives for use in drug delivery due to their optical properties and biocompatibility.We study the association between these systems and a class of drugs called fluoroquinolones, which are broadspectrum bacterial antibiotics, using fluorescence spectrophotometry and UVvisible absorption. Norfloxacin (NFX), a second generation fluoroquinolone, was chosen because it is naturally fluorescent, which facilitates the analysis of interactions without the introduction of extrinsic probes into the system. According to the literature, the association of NFX with metal ions produces changes in the properties of this drug, such as solubility and bioavailability. These changes have been evaluated as a possible solution to the problem of bacterial resistance to antibiotics. This work was divided in two parts: first, we studied the formation of the ternary complexes of NFX with copper-phenanthroline in the presence of liposomes associated to surfactants that modify the distribution of surface electric charge of the systems; in the second part, we studied the association of NFX to gold nanorods stabilized by different surfactants.

In this work, different colloidal gold nanorods were prepared dispersed in different liquid matrices. All gold nanorods were prepared from the acid tethrachloroauric (HAuCl4) in the presence of a reducing agent, using the seed mediated method. The cetyltrimethylammonium bromide (CTAB) was employed as director growth agent. The variable concentration of CTAB in the medium was evaluated in order to verify the selectivity in the formation of nanorods. In addition, we performed a kinetic study to obtain information about the formation mechanism of these particles. Colloid containing gold nanorods in organic matrices such as castor oil and hexafluorophosphate ionic liquid butylmethylilimidazolium (BMIM.PF6) were prepared in order to obtain colloid systems with different physico-chemical characteristics, however among same particles. These new colloids were obtained using the transfer technique of particles, which were synthesized in aqueous medium and then dispersed, after separation, for the desired organic matrix. All colloids were characterized by absorption spectroscopy at ultraviolet and visible (UV-Vis) and nanoparticles characterized by Transmission Electron Microscopy (TEM) / Neste trabalho, diferentes colóides contendo nanobastões de ouro dispersos em diferentes matrizes líquidas foram preparados a partir do ácido tetracloroáurico (HAuCl4), em presença de um agente redutor adequado, através do método mediado por sementes. O brometo de cetiltrimetilamônio (CTAB) foi empregado como agente direcionador de crescimento. A variável concentração de CTAB no meio foi avaliada com o objetivo de verificar a seletividade na formação de nanobastões. Além disso, foi realizado um estudo cinético para obter informações sobre o mecanismo de formação dessas partículas. Coloides contendo nanobastões de ouro em matrizes orgânicas como óleo de mamona e o líquido iônico hexafluorofosfato de butilmetilimidazólio (BMIM.PF6) foram preparados a fim de obter sistemas coloidais com diferentes características fisico-químicas porém com as mesmas partículas. Esses novos colóides foram obtidos através da técnica de transferência de partículas, as quais foram sintetizadas em meio aquoso e posteriormente dispersas, após separação, para a matriz orgânica desejada. Todos os colóides preparados foram caracterizados por Espectroscopia de absorção na região do ultravioleta e visível (UV-Vis) e as nanopartículas caracterizadas por Microscopia na eletrônica de transmissão (MET)

In recent years, organic photovoltaics (OPVs) have attracted considerable attention as a potential source of renewable energy over traditional materials due to their light weight, low production cost, mechanically stability and compatibility with flexible substrates in roll to roll processing for high volume production. In the OPVs interface plays an important role in determining the performance of the device. Interface signifies formation of efficient contact with electrode, film, and transport of free charge carrier, which results in better performance in the device. Interface engineering also helps in improving mechanical robustness of the device. Hence, understanding of interface, modification and its evaluation is important in fabrication of efficient device. In this thesis interface is modified such that the performance of the device can be improved (chapter 3 and chapter 4). In Chapter 5 and chapter 6 interface is modified such that device can be fabricated on uncommon substrate. Fabrication of device on uncommon substrates (fiber reinforced plastic and flexible glass substrate), has unique challenges. In chapter 5 and chapter 6, we look at how interface is modified to overcome the challenges associated and also understand the role of interface in improving the performance of device on such substrates is discussed. In Chapter 1 we discuss about working of organic solar cells and the challenges associated in device fabrication. Understanding of interface to overcome challenges associated is explained. It also covers brief introduction to the succeeding chapters discussed in the thesis and its recent developments. To understand the properties of interface and to analyze device performance various characterization techniques have been used are discussed in chapter 2. This chapter also covers the materials and general device fabrication techniques used in this thesis. In chapter 3, a narrow bandgap (NBG) polymer used as a near IR sensitizer in P3HT: PCBM blend. Since, P3HT with a band gap of ~1.9 eV, the commonly used p-type material absorbs approximately ~25 % of incident light. Hence, MP2 (NBG polymer) is used along with P3HT: PCBM in active layer to form a ternary blend, which helps in increased absorption. Basic properties of MP2 are evaluated using UV-visible spectroscopy, differential scanning calaorimetry(DSC), thermogravimetric analyser (TGA), gel permeation chromatography (GPC) and photoluminescence (PL) techniques. To evaluate enhanced absorption of ternary UV-visible spectroscopy is carried out. Charge transfer from one moiety to other in ternary blend is evaluated using PL and Ttime resolved microwave conductivity (TRMC). Morphology of the ternary is assessed using atomic force microscope (AFM) and structural characterization is carried out by X-ray diffraction (XRD). Performance of the device is evaluated by current-voltage (J-V) characterizations. Further improved performance is supported by external quantum efficiency (EQE). Charge extraction with linear increasing voltage (CELIV) of the device is done to evaluate the recombination mechanism in the device and to assess the performance of the device. One-dimensional (1D) ZnO nanostructures provide direct paths for charge transport, and also offer large interfacial area to make them an ideal electron transport layer. In chapter 4 highly aligned ZnO nanorods is used as electron transport layer in OPV. Growth of ZnO nanorods is two-step processes, growing seed layer and growing ZnO nanorods from hydrothermal process using an appropriate seed layer. Two different soft-chemical solution- growth methods (upward and downward) are developed to fabricate self-assembled, oriented ZnO nanorods. Substrate mounting, surface properties and optical transmittance are optimized by varying the nanorods growth conditions. Further the ZnO nanorods are UV ozone treated and its effect on performance of nanostructured buffer layer based device is evaluated. In Chapter 5 OPV is fabricated on an opaque FRP substrate. Fabrication of OPV device on opaque substrate plastic is unique and hence understanding various properties is vital. Such devices fabrication require bottom up approach, with transparent electrode as the top electrode and metal electrode on the surface of FRP. FRP has inherent rough surface of about few microns RMS roughness. In order to reduce the roughness of the substrate FRP was planarized. The planarized layer is chosen, such that it chemically binds with the substrate. The chemical interaction between substrate and planarizing coating is evaluated by FTIR and Raman spectroscopy. The binding of planarized layer and FRP is evaluated using nanoscratch technique and surface energies are studied using contact angle measurements. In addition, adhesion properties of the metal electrodes, which are deposited on planarized FRP are evaluated using nanoscratch technique. Fabrication of OPV requires a top transparent electrode. Simple spin coating technique is used to optimize the top electrode. The property of top electrode is evaluated using UV-visible spectroscopy for transmittance, and sheet resistance of the electrode is characterized. OPV device is fabricated on planarized FRP substrate using optimized top transparent electrode and its PV properties is evaluated. Performance of the device is evaluated for two different bottom electrodes and further performance of device is enhanced using buffer layers. Usually flexible OPVs are fabricated on plastic substrate such as PET, PEN. However they are not structurally stable at high temperatures and have high oxygen and moisture Permeability. In Chapter 6 Organic based photovoltaic devices were fabricated on flexible glass. Flexible glass has high strength and it is also known for low oxygen and moisture permeability. Fabrication of device on flexible glass has never been done before and hence, generation of data is necessary for commercialization of the technology. Device fabrication is optimized by using two different transparent conducting layers (ITO- sputter deposited, PEDOT: PSS-solution processed) and device performance was evaluated for both. Since the substrate is flexible in nature understanding the performance of the device during flexing is important. For this 2-parallel plate flexural apparatus is fabricated for in-situ measurements along with current voltage measurements. These devices are flexed cyclically and performance of device is evaluated. Therefore, work discussed in the thesis show by modifying the interface of the device, and understanding various interfaces of the device is crucial for improving the performance of the device. Also by engineering the interface, devices can be fabricated on various types of substrate.

Orientador: Prof. Dr. Mauro Coelho dos Santos / Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Ciência e Tecnologia/Química, 2018. / Este trabalho visou sintetizar eletrocatalisadores baseados em nanobarras de céria (NR CeO2) suportadas em carbono Vulcan XC-72, em diferentes proporções mássicas. Caracterizar e avaliar suas eficiências, na reação de redução de oxigênio (RRO) tendo como objetivo o mecanismo 2-elétrons, ou seja, a eletrogeração de H2O2, pela técnica de eletrodo de disco-anel rotatório (RRDE). Além disso, realizaram-se as confecções de eletrodos de difusão gasosa (EDG) com o eletrocatalisador mais promissor tendo em vista a avaliação da capacidade de produção de H2O2, em comparação a um EDG de carbono Vulcan XC-72 aplicando-se em processos eletroquímicos oxidativos avançados (PEOAs) na degradação do paracetamol. Pelo estudo da RRO utilizando a técnica de RRDE, concluiu-se que houve uma grande melhora na eletrogeração de H2O2 suportando 1% de NR CeO2 no carbono Vulcan XC-72 devido ao efeito sinérgico entre baixa concentração de NR CeO2 e o carbono Vulcan XC-72. Esse eletrocatalisador mostrou um menor potencial de início da RRO, quando comparado ao do carbono Vulcan XC-72, com transferência de 2,1 elétrons na RRO e conversão de 95% do gás oxigênio (O2) em H2O2, enquanto o carbono Vulcan XC-72 foi capaz de converter apenas 54% de O2 em H2O2. O EDGCe confeccionado produziu 1463 mg L-1 de H2O2, enquanto o EDGV produziu apenas 490 mg L-1, em 2 horas de eletrólise no potencial -2,7 V vs. Ag/AgCl. O EDGCe foi aplicado em diferentes PEOAs visando a mineralização do paracetamol em uma célula eletroquímica de 350 mL, com taxas de mineralização de até 98,4% após 6 horas, o que indica ser um promissor EDG a ser utilizado em PEOAs. / This work aimed to synthesize electrocatalysts based on ceria nanorods (CeO2 NR) supported on Vulcan XC-72 carbon, in the different mass proportions. Characterize and evaluate its efficiencies, in the oxygen reduction reaction (ORR) aiming the 2-electron mechanism, ie, H2O2 electrogeneration, by the rotating ring-disc electrode (RRDE) technique. In addition, the gas diffusion electrodes (GDE) were made with the most promising electrocatalyst having as reference the evaluation of the H2O2 production capacity, compared to a Vulcan XC-72 carbon GDE applying in electrochemical advanced oxidative processes (EAOPs) in the degradation of paracetamol. By the ORR study using the RRDE technique, it was concluded that there was a great improvement in the H2O2 electrogeneration supporting 1% of CeO2 NR in the Vulcan XC-72 carbon due to the synergistic effect between low concentrations of NR CeO2 and Vulcan XC-72 carbon. This electrocatalyst showed a lower initial potential of ORR, when compared to of the Vulcan XC-72 carbon, with transfer of 2.1 electrons and conversion rate of 95% of the oxygen gas (O2) into H2O2, while the Vulcan XC-72 carbon was able to convert only 54% of O2 into H2O2. The prepared GDECe produced 1463 mg L-1 of H2O2, while GDEV produced only 490 mg L-1 of H2O2, in 2 hours of electrolysis in the potential -2.7 V vs. Ag/AgCl. The GDECe was applied in different EAOPs aiming at the mineralization of paracetamol in a 350 mL electrochemical cell, with mineralization rates up to 98.4% after 6 hours, indicating that it is a promising GDE to be used in EAOPs.

Submitted by Erika Demachki (erikademachki@gmail.com) on 2015-01-16T17:12:14Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Maciel Salomão de Almeida - 2013.pdf: 7583295 bytes, checksum: 760412dd4823f72e941a9b42de2513e8 (MD5) / Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2015-01-16T17:36:50Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Maciel Salomão de Almeida - 2013.pdf: 7583295 bytes, checksum: 760412dd4823f72e941a9b42de2513e8 (MD5) / Made available in DSpace on 2015-01-16T17:36:50Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Maciel Salomão de Almeida - 2013.pdf: 7583295 bytes, checksum: 760412dd4823f72e941a9b42de2513e8 (MD5) Previous issue date: 2013-07-26 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / The method of obtaining nanorods was conducted by precipitation of hydroxides of samarium and gadolinium weak base with ammonium hydroxide at room temperature and subsequent calcination of hydroxides to oxides. For the nanosized powders hydroxide with nanorods morphology was used hydrothermal system assisted by microwave (HTMW). The products obtained were characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The application of X-ray diffraction identified crystalline phases, quantitation of phases, determining the parameters of the unit cell, the crystallite size and orientation. The scanning electron microscopy and transmission contributed to the morphological observations in the post hydroxide nanorods. Obtaining oxides occurred after the thermal analysis: Thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The gadolinia and samaria, are known as oxides of these elements were obtained by dehydration of the respective hydroxides. During calcination of the hydroxides, the porosity of the nanorods became increasingly smaller due to reduction of surface free energy of the nanorods, maintaining the morphology. / O método de obtenção dos nanobastões foi realizado por precipitação dos hidróxidos de samário e gadolínio, com a base fraca de hidróxido de amônio, à temperatura ambiente e posterior calcinação dos hidróxidos a óxidos. Para obter os pós nanométricos de hidróxidos, com morfologia em nanobastões foi utilizado o sistema hidrotérmico assistido por micro – ondas (HTMW). Os produtos obtidos foram caracterizados por difração de raio X, microscopia eletrônica de varredura, (MEV) e microscopia eletrônica de transmissão (MET). A aplicação da difração de raios X identificou as fases cristalinas, a quantificação de fases, a determinação dos parâmetros da cela unitária, a orientação e o tamanho do cristalito. As microscopias eletrônicas de varredura e transmissão contribuíram para as observações morfológicas em nanobastões dos pós de hidróxidos. A obtenção dos óxidos ocorreu após as análises térmicas: análise termogravimétrica (TGA) e análise térmica diferencial (DTA). A samária e a gadolínia, como são conhecidos os óxidos destes elementos, foram obtidas pela desidratação dos seus respectivos hidróxidos. Durante a calcinação dos hidróxidos, a porosidade dos nanobastões se tornou cada vez menor, devido à redução da energia livre superficial dos nanobastões, mantendo sua morfologia.

In this work, different optical techniques have been explored to study and characterize crude oil and its asphaltene. Crude oil is extremely complex fluid used to produce fuel for a wide range of applications. The characterization of this fluid is key for optimum operations in the oil and gas industry. First, we demonstrate the application of gold nanorods in characterizing a different set of crude oils. We utilize the high sensitivity of the Localized Surface Plasmon Resonance (LSPR) of the nanorods to the surrounding environment to measure the crude oil refractive index. We immobilized the nanorods on a glass substrate and took the measurement in a reflection configuration. The setup and the nanorods were calibrated using different fluids with known refractive index, and a sensitivity of 247 nm/RIU and a resolution of 0.013 RIU have been achieved. In addition to the simplicity of this approach, it has eliminated the absorption issue and made it possible to measure high optical density crude oils with typical Visible-NIR wavelengths. Surface-Enhanced Raman Spectra (SERS) can also be measured. SERS can provide additional useful information, especially to some applications such as downhole fluid analysis, where confirmation of the hydrocarbons presence is necessary. In the second part of this work, we used Terahertz Time-Domain Spectroscopy (THz-TDS) to study the asphaltene in three different crude oils. THz-TDS has a feature of measuring the amplitude and time delay and consequently the refractive index and absorption coefficient spectra simultaneously. Our approach is based on measuring the THz signal from neat crude oil samples and comparing it with the THz signal after removing the asphaltene from the samples (maltene). The results show that the difference in the time delay and the peak amplitude between the neat oil and the maltene have a linear relation with the asphaltene content. The refractive index spectra of different asphaltenes show variation in the low THz frequencies and comparable spectra in the higher frequencies. The absorption of asphaltene was mild and no distinctive absorption feature was observed except for some narrow absorption peaks that we attributed to water molecules adsorbed on the asphaltene. / Graduate

Raman spectroscopy is employed by NASA, and many others, to detect trace amounts of substances. Unfortunately, the Raman signal is generally too weak to detect when very small, but non-trivial, amounts of molecules are present. One way around this weak signal is to use surface enhanced Raman spectroscopy (SERS). When used as substrates for SERS, metallic nanorods grown using physical vapor deposition (PVD) provide a large enhancement factor to the Raman signal, as much as 1012. However, Silver (Ag) nanorods that give high enhancement suffer from rapid degradation as a function of time and exposure to harsh environment. Exposure to harsh environments is an enormous issue for NASA; considering all environments experienced during space missions will be drastically different from Earth regarding atmosphere pressure, atmosphere composition, and environmental temperature. Au and Ag nanorods suffer from a thermochemical kinetic phenomenon where the surface atoms diffuse and cause the nanostructures to coalesce towards bulk structure. When in bulk, SERS enhancement is lost and the substrate becomes useless. A stable structure for SERS detection is designed through engineering the barriers to surface diffusion. Aluminum (Al) nanorods are forced to undergo surface diffusion through thermal annealing and form rough mounds with a stable terminating oxide layer. When Ag is deposited on top of this Al structure, it becomes kinetically bound and changes to physical structure become impeded. Using this paradigm, samples are grown with varied lengths of Ag and are then characterized using scanning electron microscopy (SEM) and Ultraviolet-Visible spectroscopy. The performance of the samples are then tested using SERS experiments for the detection of trace amounts of rhodamine 6G, a ‘gold standard’ analyte. Characterization shows the effectiveness of the Raman substrates remains stable up to 500°C. Transitioning to basic scientific investigation, next is to strive to isolate the individual impacts of chemical and physical changes to the Ag nanostructure and how they affect the Raman signal. Substrates are compared over the course of a month long experiment to determine the effects of vacuum storage and addressing the effects of chemical adsorbance. Additionally, this was attempted by comparing the signal degradation of Ag nanorods to that of Au, which is known to be chemically inert, allowing for the separation of chemical and physical effects. Although Ag and Au have similar melting points, Ag physically coarsened significantly more. FTIR also showed significant chemical contamination of the Ag, but not Au. A hypothesis is proposed for future investigations into the chemical changes and how they are coupled with and promote the physical changes in nanostructures. Overall, the novel SERS substrate engineered here may enable the detection of trace amounts of molecules in harsh environments and over long timescales. Conditions such as those found on space missions, where substrates will experience months or years of travel, high vacuum environments, and environments of extreme temperatures.

In this thesis, synthesis, characterization and electrical transport of Carbon nanotubes (CNTs) have been discussed. The first chapter contains a brief introduction of various forms of carbon including CNT. The CNTs are currently the materials of intense research interest due to their remarkable mechanical and electrical properties. CNTs can be visualized as a graphene sheet that has been rolled into a seamless tube. CNTs are either single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes (MWCNT). SWCNT is a tube with only one wall and MWCNT has many coaxial tubes and weak Van der Waal forces hold them together. The properties depend on chirality, diameter and length of the tubes. Chirality is defined by the symmetry and the chiral angle formed between the carbon bonds. The atomic structure of CNTs is described in terms of the tube chirality, which is defined by the chiral vector Ch and the chiral angle . The chiral vector is Ch = na1 + ma2, where the integers (n, m) are the number of steps along the zig-zag carbon. Depending on the tube chirality the electrical properties of the CNTs differ; they can be metallic or semiconducting. When n-m = 3p, where p is an integer, the CNTs are metallic and when n-m  3p, the CNTs are semiconducting. Due to the high anisotropy and high aspect ratio, CNTs have many potential applications with great technological importance such as functionalized molecules, conductive wires, bearings of rotational motors, field emitters, hydrogen storage, sensors, polymer composites, nanotube yarn and nanotube filters, X-ray generator, electron sources for microscopy and lithography, gas discharge tubes and vacuum microwave amplifiers, etc. The first chapter gives a brief introduction about various forms of carbon and their properties, particularly of CNTs. The nature of the CNTs depends on the method of production, which controls the degree of graphitization, the tube diameter and the chirality. Most synthesis methods originate from the idea of obtaining adequately active carbon atomic species or clusters from carbon sources and assembling them into CNTs without or with catalysts. The commonly used methods for the synthesis of carbon nanotubes are arc-discharge, Laser ablation, high-pressure catalytic decomposition of carbon monoxide (HiPCO), electrophoretic deposition (EPD), flame synthesis, pyrolysis, chemical vapour deposition (CVD), hot-filament CVD, plasma enhanced chemical vapour deposition (PECVD) using DC, RF, and micro wave power sources, hot-filament dc (HF-dc PECVD), inductively coupled plasma (ICPECVD) and electron cyclotron resonance (ECR PECVD). Although many efforts have been made to develop various synthesis methods, most of them require many steps. Moreover, the complicated and rigorous control of parameters and expensive materials are unavoidable that has put limitation in reproducing the same in large scale. In this chapter, a simple method for the synthesis of CNTs on a large scale that eliminates nearly the entire complex and expensive machinery associated with widely used growth techniques has been discussed. In Chapter 2, the synthesis and characterization of entangled CNTs are discussed. It is shown that entangled CNTs can be synthesized in one step by using double stage furnace. Tetrahydrofuran as carbon source material and nickelocene as catalyst source material have been used to synthesize CNTs. With this method CNTs can be synthesized at a temperature as low as at 600 0C. In this technique the self-developed pressure carries the vapours to the hot zone of the furnace. This has led to think in modifying the double stage furnace. A single stage furnace having temperature gradient is made to synthesize CNTs. The vapours are carried from low temperature zone to hot zone where the carbon species and catalysts react to form CNTs. The advantage of this furnace is that it is one-step process. Using another carbon source material such as Diethyl Ether and nickelocene as catalyst source material CNTs are synthesized. The as synthesized and purified CNTs are characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), transmission electron microscope (TEM), high resolution TEM (HRTEM) and Raman spectroscopy. The CNTs are multi-walled in nature as observed by HRTEM. In Chapter 3, the synthesis of aligned CNTs is discussed by using benzene as carbon source and ferrocene as catalyst source materials. Aligned MWCNTs were synthesized in the temperature range between 650 - 1100 0C in a single stage furnace without the need for carrier gas nor predeposited metal catalyst substrate. The essential need of CNTs are (1) to obtain aligned nanotubes with millimeter lengths to enable the formation of novel nanotube-polymer composites that incorporate continuous nanotubes throughout their thickness for highly anisotropic thermal and electrical conductivities; and (2) to provide samples for detailed physical characterization - tensile strength, thermal, electrical conductivity, field emission etc. SEM observation reveals the increase in length of nanotubes from 85 m to 1.4 mm with the increase of preparation temperature. The diameter as investigated by high-resolution transmission electron microscopy (HRTEM) remains almost constant 70-80 nm (75-85 layers). Once nanotube formation is established, the growth continues in the same direction and may well be reinforced by the presence of surrounding CNTs i.e. almost every particle produces a nanotube and bundling of neighboring tubes lead to collective vertical growth. The increase in length is due to the enhanced diffusion of active carbon with increasing preparation temperatures. The alignment of CNTs is also observed to the lateral side of the substrate. In Chapter 4, the synthesis and characterization of carbon nanoribbon and singled crystal iron filled CNTs is discussed. Particularly interesting are those CNTs filled with magnetic nanowires, which can provide an effective barrier against oxidation and consequently ensure a long-term stability in the core. The filling of metals within carbon nanotubes has extended the potential application base of these materials to quantum memory elements, high density magnetic storage media, semiconducting devices, field electron emitters, high resolution magnetic atomic force microscopy tips, magnetic field sensors and scanning probe microscopes etc. Tetrahydrofuran as carbon source material and ferrocene as catalyst materials has been used to synthesize mixture of carbon nanoribbons and iron filled CNTs. The techniques used to characterize the materials are XRD, SEM, HRTEM and superconducting quantum interference device (SQUID). The powder XRD pattern shows that the bcc -Fe phase of iron is present. HRTEM studies reveal the presence of multi-walled carbon nanotubes and well-crystallized -Fe phase filled inside the core region. Closer inspection of the HRTEM images indicated that the bcc structure -Fe nanowires are monocrystalline and Fe (110) plane is indeed perpendicular to the G (002) plane. Large coercivity (i.e. 1037 Oe at 300 K and 2023 Oe at 10 K) in the iron filled CNTs and carbon nanoribbons have been observed. The high coercivity is mainly attributed to the following two factors. Firstly, it is known that due to the uniaxial magnetic anisotropy of the nano size iron in the core region of the carbon nanotubes. Secondly, ferromagnetic behavior exhibited by the localized states at the edges of the carbon nanoribbons. The anisotropic electrical transport property of MWCNTs has been discussed in the chapter 5. The activated diffusive nature of transport along axial direction of CNT is explained. The transport perpendicular to the tube direction is explained in terms of a hopping mechanism. The anisotropic resistivity (N/P) value obtained is 3. The temperature dependent magnetoresistance (MR) is studied in magnetic fields up to 11 Tesla at low temperatures both in the parallel and perpendicular direction of an aligned MWCNT mat. In both cases a negative MR is observed. Chapter 6 discusses the preparation of CNT-polymer composites. The temperature dependence of the conductivity and magnetoresistance (MR) has been studied making four-point contact method on the carbon nanotubes polymer composites as result of increasing CNT content. The conductivity increases with increasing carbon nanotube weight percentage. The increase in conductivity as a function of the CNT weight percent is attributed to the introduction of conducting CNT paths in the polymer matrix. With the increasing CNT content the number of interconnections present in a random system is found to vary. Electrical conduction in nanotube mat or nanotube composites is explained by a variable range hopping (VRH) conduction mechanism. The negative magnetoresistance has been observed for the polymer composites. It is consistent with the report on CNTs bundles and polymer composites. Finally a brief summary of the work presented in this dissertation is discussed along with future directions in this research.

Recently, efforts have been made for self-powering the batteries and portable electronic devices by piezoelectric nanogenerators. The piezoelectric nanogenerators can work as a power source for nano-systems and also as an active sensor. The piezoelectric nanogenerator is a device that converts random mechanical energy into electrical energy by utilizing the semiconducting and piezoelectric properties. Also, the mechanical energy is always available in and around us for powering these nano devices. The aim of the present thesis work is to explore 1D and 2D ZnO nanostructures (nanorods and nanosheets) on metal alloy substrates for the development of piezoelectric nanogenerators in energy harvesting and sensors applications. Hydrothermal synthesis method was adopted for the growth of ZnO nanostructures. The nanogenerators were fabricated by using the optimized synthesis parameters and subsequently studied their performance for power generation and as an active speed sensor. These 1D and 2D nanostructures based nanogenerators have opened up a new window for the energy harvesting applications and sensors development. The thesis is divided into following six chapters. Chapter 1: This chapter gives a general introduction about energy harvesting devices such as nanogenerators, available energy sources, mechanical energy harvesting, ZnO material and the details on hydrothermal synthesis process. A brief literature survey on different applications of piezoelectric nanogenerators is also included. Chapter 2: A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. Details on the synthesis of 1D ZnO nanorods on Phynox alloy substrate by hydrothermal method are presented. Further, the optimization of parameters such as growth temperature, seed layer annealing and substrate temperature effects on the synthesis of ZnO nanorods are discussed in detail. As-synthesized ZnO nanorods have been characterized using XRD, FE-SEM, TEM and XPS. Chapter 3: It reports on the fabrication of piezoelectric nanogenerator on Phynox alloy substrate as power generating device by harvesting the mechanical energy. Initially, the performance of the nanogenerator for power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the output voltage response of the nanogenerator was studied for its use as an active speed sensor. Chapter 4: Synthesis of Al doped 2D ZnO nanorsheets on Aluminum alloy (AA-6061) substrate by hydrothermal method is reported in this chapter. The optimized parameters such as growth temperature and growth time effects on the synthesis of ZnO nanosheets are discussed. As-synthesized ZnO nanosheets were characterized using XRD, FE-SEM, TEM and XPS. The Al doping in ZnO is confirmed by EDXS and XPS analysis. Chapter 5: Cost effective fabrication of Al doped 2D ZnO nanosheets based nanogenerator for direct current (DC) power generation is reported in this chapter. The performance of the nanogenerator for DC power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the DC output voltage response of the nanogenerator was studied for its use as an active speed sensor. Chapter 6: The first section summarizes the significant features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.