Plasma-enhanced chemical vapor deposition of carbon nanofibers: correlations between process parameters and physicochemical properties
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School of Electrical Engineering |
Doctoral thesis (article-based)
| Defence date: 2024-08-21
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Authors
Date
2024
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Mcode
Degree programme
Language
en
Pages
76 + app. 72
Series
Aalto University publication series DOCTORAL THESES, 143/2024
Abstract
Carbon nanofibers (CNFs) possess versatile physicochemical properties, making them pivotal in advancing technology, particularly in electrochemical sensing due to their high conductivity, large surface area, and broad potential window. Plasma-enhanced chemical vapor deposition (PECVD) is commonly employed for CNF synthesis, facilitating the growth of vertically aligned fibers at low temperatures. This intricate process involves adjusting parameters such as temperature, gas ratio, and plasma power to tailor fiber morphology and surface chemistry. Catalyst and adhesive layer selection further impacts these properties, while growth time serves as an additional tunable parameter. Despite extensive documentation of CNF growth via PECVD, systematic investigations into key aspects are lacking. For instance, the influence of the adhesive layer on CNF morphology, surface chemistry, and electrochemical performance remains unexplored. Similarly, the dual role of NH3 as both etchant and dopant is often overlooked. Moreover, discussions on CNF applications rarely justify process parameter selection or explore potential enhancements through parameter adjustments. The aim of this work is to systematically assess (i) the effects of material choices and selected process parameters on the micro- and macroscale morphology, surface chemistry, and doping of CNFs, and (ii) the implications of these effects on their electrochemical characteristics. Two research hypotheses guide the work done in this thesis, namely, (I) the choice of adhesive layer significantly influences the morphology, surface chemistry, and electrochemical performance of CNFs grown via PECVD, and (II) alternating between H2 and NH3 as etchant gases during CNF growth alters both micro- and macroscale morphology, impacting electroanalytical properties. Our key findings confirm our hypotheses: (i) CNF morphology, surface chemistry, and electrochemical properties depend on the adhesive layer, (ii) CNF macroscale geometry affects pseudocapacitance without significantly impacting electron transfer kinetics, (iii) precise control of CNF morphology enhances selectivity and sensitivity towards our probe molecule dopamine, and (iv) altering etchant gases between H2 and NH3 significantly alters CNF micro- and macroscale morphology, resulting in notable changes in electrochemical properties, and (v) the ratio of the etchant and feedstock gases influences the doping level, morphology and electrochemical characteristics of CNFs. Overall, our results demonstrate the importance of carefully selecting the process parameters in the CNF growth process, as the choice has a marked effect on the doping, morphology, surface chemistry and electrochemical performance of the CNFs. By demonstrating that the electroanalytical performance of CNF electrodes can be tailored by this approach, this work provides a robust foundation for designing CNF electrodes for a wide variety of applications.Description
Supervising professor
Laurila, Tomi, Prof., Aalto University, Department of Electrical Engineering and Automation, FinlandThesis advisor
Laurila, Tomi, Prof., Aalto University, Department of Electrical Engineering and Automation, FinlandKeywords
carbon nanofiber, plasma-enhanced chemical vapor deposition
Other note
Parts
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[Publication 1]: Pande, Ishan; Pascual, Laura Ferrer; Kousar, Ayesha; Peltola, Emilia; Jiang, Hua; Laurila, Tomi. 2023. Interface matters - Effects of catalyst layer metallurgy on macroscale morphology and electrochemical performance of carbon nanofiber electrodes. Diamond and Related Materials, volume 131, pages 109566.
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202212227254DOI: 10.1016/J.DIAMOND.2022.109566 View at publisher
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[Publication 2]: Pande, Ishan; Sainio, Sami; Sainio, Jani; Liljeström, Ville; Jiang, Hua; Laurila, Tomi. 2023. Correlation between microstructure and surface chemistry of carbon nanofibers grown using different adhesive layers. Diamond and Related Materials, volume 133, pages 109713.
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202302202120DOI: 10.1016/J.DIAMOND.2023.109713 View at publisher
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[Publication 3]: Pande, Ishan; Pascual, Laura Ferrer; Kousar, Ayesha; Sainio, Jani; Jiang, Hua; Laurila, Tomi. 2024. Effect of etchant gases on the structure and properties of carbon nanofibers. Diamond and Related Materials, volume 144, pages 111004.
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202403272932DOI: 10.1016/j.diamond.2024.111004 View at publisher
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[Publication 4]: Pascual, Laura Ferrer; Pande, Ishan; Kousar, Ayesha; Rantataro, Samuel; Laurila, Tomi. 2022. Nanoscale engineering to control mass transfer on carbon-based electrodes. Electrochemistry Communications, volume 140, pages 107328.
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202208104610DOI: 10.1016/J.ELECOM.2022.107328 View at publisher
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[Publication 5]: Kousar, Ayesha; Pande, Ishan; Pascual, Laura Ferrer; Peltola, Emilia; Sainio, Jani; Laurila, Tomi. 2023. Modulating the Geometry of the Carbon Nanofiber Electrodes Provides Control over Dopamine Sensor Performance. Analytical Chemistry, volume 131, pages 2983-2991.
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202302082036DOI: 10.1021/acs.analchem.2c04843 View at publisher
- [Publication 6]: Pande, Ishan; Nekoueian, Khadijeh; Sainio, Jani; Laurila, Tomi. Modifying the morphology, doping, and electroanalytical performance of carbon nanofibers by varying the ratio of etchant and feedstock gases. Submitted to Journal of Electroanalytical Chemistry (May 2024).