1,720,990 research outputs found
Photonic Systems Based on Carbon Nanotubes: Photoluminescence Enhancement and Saturable Absorbers by Inkjet Printing and Integration on Fibre Tapers
Get PDFThe multifunctional properties of single-wall carbon nanotubes (SWNTs) created a robust platform for unprecedented innovations in a variety of applications in photonics, sensors, electronics, smart manufacturing and drug delivery. This thesis presents an experimental study of the author’s research using innovative approaches for the development of photonic systems based on SWNTs’ dispersions and composites, featuring enhanced and effective optical properties. The first set of experiments demonstrates a novel approach for the enhancement of SWNTs’ photoluminescent (PL) properties via complexation with organic dyes. One of the more significant findings to emerge from this investigation is the interaction of the indopentamethinedioxaborine dye (DOB-719) with SWNTs, which resulted in new optical features in the spectral range of the intrinsic excitation of the dye, providing clear evidence of the resonance energy transfer from DOB-719 to the SWNTs. The findings from this study allowed for the proposal of the mechanism of interaction between the SWNT and DOB-719, where the dye is attracted to the SWNT surface via π-π stacking with the hydrophobic part facing the aqueous medium by polar groups. The second set of experiments examined a limitation imposed by the use of SWNT-polymer composites for saturable absorber (SA) applications. The integration of this device in the fibre cavity resulted in modification of the composite properties under continuous high power laser irradiation, which limits the use of composites to generate ultrashort pulses with stable parameters for a long operation time (>10,000 hours). This stimulated the design of advanced approaches in this work as an alternative to the composite method. The first approach describes a method for the controllable integration of SWNT directly on the core of a fibre edge, using the inkjet printing technique. It is important to note that a direct correlation between the number of printed layers and properties of SA was determined, showing that a SA with 20,000 layers gives the best parameters. The obtained output power and pulse energy are higher than all earlier reported results on SA for erbium-doped fibre lasers using sandwiched SWNT- composites. The second approach is to coat the tapered fibre with a low refractive index SWNT-polymer composite. This method depends on lateral interaction with the evanescence field of the propagating pulse in the laser cavity. The study reports SAs devices with controllable saturation intensity, low losses and large saturable to non-saturable loss ratios
Study of Electrodeposition Method to Produce Carbon Nanotubes
Get PDFSince its first observation, Carbon Nanotubes (CNT) has drawn considerable research interest. Numerous investigations revealed outstanding properties for this unique form of carbon. Its remarkable characteristics include its electronic properties, thermal conductivity, and mechanical properties offer tremendous new opportunities and applications, often described as technological marvels. Nevertheless, like other new materials, CNT faces the transfer phenomenon from marvel material to market driven by its profitability or marketability. From the market perspective, the need for carbon nanotubes increases each year, while in the manufacturing view, production is plateauing. Therefore the gap between supply and demand exists, and the commercial viability of CNTs seems assured. However, the market's growth will depend on the efficiency in tackling dominant factors such as price to be competitive. No matter how excellent new materials are, the requirement of cheap to produce, consistent quality, easy handle and toxicity tolerance were always the rule. This study presents the Electrodeposition method as an alternative method to producing Multiwalled Carbon Nanotubes (MWCNT) utilising CO2 as carbon feedstock. Four approaches are discussed in this thesis: Literature review, Molecular dynamics, and experiments using Taguchi and OFAT (One Factor at a Time). Electrodeposition is a method that utilises molten salt, atmospheric CO2, and electrodes that can perform without catalyst preparations. At the same time, the requirements of well-established methods such as Arc Discharge, Laser Ablation, and Chemical Vapour Deposition result in a less cost-effective product and are challenging to scale up. In arc discharge, pure graphitic carbon soot can be utilised to synthesise CNT, but the addition of catalysts and preparation is required to produce a large amount of CNT. However, the electrode size and high current proportion are limited even with the extra preparation process. Laser ablation produces high-quality CNT with the limitation of its laser power requirement, while preparing catalyst in CVD also adds time or labour cost. The literature review in this study concludes that Electrodeposition can produce carbon nanotubes in an uncomplex way due to preparation ease. Electrodeposition does not have the limitation of the previous process and is arguably easier to scale up. However, this method has some challenges that need to be addressed, most related to synthesis parameters. In the previous research, the study is conducted partially and comparing the result is sometimes unusable since each investigator weighs in some value over another. For example, yield is measured in the purity or weight of the end product, and other research considers the CNT growth area or catalyst-CNT ratio in the system. In this research, Molecular dynamics, Taguchi and OFAT (One Factor at a Time) methods counter the challenges by providing a thorough study. Molecular dynamics determine the base behaviour expected from variables, focusing only on parameter changes that affect the carbon bonds formed in the electrodeposition system. Furthermore, Taguchi and OFAT are used to optimise variables and examine the end-product properties of each variable on an experiment basis. From molecular dynamics, it is found that the carbon bond created is affected by the total energy in the system, while total energy depends on variable value. Under the theoretical models used in the simulation, increasing parameters value which includes temperature, external potential, Carbon number in the system, and synthesis time, increases the carbon bond created in the system. Furthermore, changing the cathode from Ni to Cu decreases the carbon bond formed. Using the Taguchi method L25 design with five parameters, optimisation was conducted. The optimisation result is not as linear as the expectations of the Molecular dynamic and revealed that other factors, such as the Expansion of molten salt, conductivity gain, current instability, and excessive carbon debris, play roles in the system. The use of metal alloys was essential to promote CNT, as suggested in the previous investigation, which is supported in this thesis. Further evidence of better performance electrode metal alloys is found in Taguchi and OFAT, in which Zn alloys dominated early research. The OFAT also present the end-product characterisation under parameter changes utilising XRD, FTIR, Raman SEM, and EDX analysis. Using the Taguchi method L25 design with five parameters, optimisation was conducted. The optimisation result is not as linear as the expectations of the Molecular dynamic and revealed that other factors, such as the Expansion of molten salt, conductivity gain, current instability, and excessive carbon debris, play roles in the system. The use of metal alloys was essential to promote CNT, as suggested in the previous investigation, which is supported in this thesis. Further evidence of better performance electrode metal alloys is found in Taguchi and OFAT, in which Zn alloys dominated early research. The OFAT also present the end-product characterisation under parameter changes utilising XRD, FTIR, Raman SEM, and EDX analysis
Detection and Characterisation of Micro- and Nano-plastics in Water using Optical Spectroscopy
Get PDFMicro- and nanoplastic (MNP) contamination in various environmental matrices has become an increasing global concern due to its potential ecological and health impacts. However, detecting and characterising these minuscule plastic particles remains challenging due to the limitations of conventional spectroscopic techniques. This thesis explores the potential of photoluminescence (PL) spectroscopy as an alternative technique for detecting and characterising MNPs in aqueous media. The research encompasses the optimisation of fluorescence excitation-emission (FLE) features for MNP detection, the development of a protocol for generating model MNPs, and the proof-of-concept demonstration of a semi-portable PL spectrometer for microplastic detection. In the first set of experiments, Fluorescence (FL) spectroscopy was utilised to investigate the intrinsic excitation-emission features of common microplastics, including polystyrene (PS), polyethylene terephthalate (PET), and polypropylene (PP). Through systematic analysis, distinct fluorescence signatures were identified for each polymer type, enabling precise and label-free identification. These spectral characteristics, linked to polymer-specific molecular transitions, form the basis for a non-destructive fluorescence-based microplastic detection method. The second set of experiments established a protocol for generating model MNPs through a high-power direct ultra-sonication technique. This method significantly improved the efficiency of MNP production compared to conventional methods, eliminating the need for chemical additives and achieving high suspension stability in an aqueous medium. The generated MNPs, ranging from 100 nm to 150 μm, closely resembled environmental plastic pollutants in terms of size distribution and morphology. Their characterisation using Raman spectroscopy, infrared spectroscopy combined with machine learning, UV-Vis spectroscopy, and SEM imaging confirmed their suitability as reference materials for microplastic research. Furthermore, the third phase of the study examined the effectiveness of FLE mapping for detecting and characterising MNPs in aqueous media. The study demonstrated that ultrasonicated MNPs, including PS, PET, and PP exhibited strong and distinct FL spectra, including those smaller than 100nm. This study confirmed that optimised excitation wavelengths provide distinct FL fingerprints for MNPs and enhance their FL signal strength, improving the technique's sensitivity for real-time detection. Finally, the development of a semi-portable PL spectrometer further highlighted the feasibility of real-time, on-site MNP detection. Although challenges such as background noise require further optimisation, this proof-of-concept system represents a significant step toward field-deployable MNP pollution monitoring
Functional carbon nanotubes for photonic applications
Get PDFCarbon nanomaterials are an active frontier of research in current nanotechnology. Single wall Carbon Nanotube (SWNT) is a unique material which has already found several applications in photonics, electronics, sensors and drug delivery. This thesis presents a summary of the author’s research on functionalisation of SWNTs, a study of their optical properties, and potential for an application in laser physics. The first significant result is a breakthrough in controlling the size of SWNT bundles by varying the salt concentrations in N-methyl 2-pyrrolidone (NMP) through a salting out effect. The addition of Sodium iodide leads to self-assembly of CNTs into recognizable bundles. Furthermore, a stable dispersion can be made via addition polyvinylpyrrolidone (PVP) polymer to SWNTs-NMP dispersion, which indicates a promising direction for SWNT bundle engineering in organic solvents. The second set of experiments are concerned with enhancement of photoluminescence (PL), through the formation of novel macromolecular complexes of SWNTs with polymethine dyes with emission from enhanced nanotubes in the range of dye excitation. The effect appears to originate from exciton energy transfer within the solution. Thirdly, SWNT base-saturable absorbers (SA) were developed and applied to mode locking of fibre lasers. SWNT-based SAs were applied in both composite and liquid dispersion forms and achieved stable ultrashort generation at 1000nm, 1550nm, and 1800 nm for Ytterbium, Erbium and Thulium-doped fibre laser respectively. The work presented here demonstrates several innovative approaches for development of rapid functionalised SWNT-based dispersions and composites with potential for application in various photonic devices at low cost
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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