• Pande, Ishan

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. <br/><br/>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. <br/><br/>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. <br/><br/>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.

Topics

• impedance spectroscopy
• surface
• Carbon
• chemical vapor deposition
• aligned