Public defence in Electronics integration and reliability, M.Sc. Ishan Pande

The title of the thesis: Plasma-enhanced chemical vapor deposition of carbon nanofibers: Correlations between process parameters and physicochemical properties 

Doctoral student: Ishan Pande
Opponent: Prof. Thomas Wågberg, Umeå University, Sweden
Custos: Prof. Tomi Laurila, Aalto University School of Electrical Engineering, Department of Electrical Engineering and Automation

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. Electrochemical sensors are increasingly important today for their potential impact on diagnosing and treating neurological diseases. Plasma-enhanced chemical vapor deposition (PECVD) is frequently utilized 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, publications concerning CNF applications rarely justify process parameter selection or explore potential enhancements through parameter adjustments. 

The aim of this work is to systematically assess the effects of material choices and selected process parameters on the micro- and macroscale morphology, surface chemistry, and doping of CNFs. Furthermore, the implications of these effects on the electrochemical properties of CNFs are explored. Our findings reveal that the selection of adhesive layer materials and etchant gases has a significant impact on the morphology, surface chemistry and electrochemical properties of CNFs. Moreover, we demonstrate that precise control of CNF morphology enhances selectivity and sensitivity towards dopamine. 

Furthermore, we show that the ratio of etchant and feedstock gases influences the morphology, doping and electrochemical characteristics of CNFs. Overall, our results highlight the importance of carefully selecting process parameters in the CNF growth process, as these choices markedly affect the doping, morphology, surface chemistry, and electrochemical performance of CNFs. By demonstrating that the electroanalytical performance of CNFs can be tailored through this approach, this work provides a robust foundation for designing CNF electrodes for a wide variety of applications.

Keywords: Carbon nanofiber, plasma-enhanced chemical vapor deposition

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

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Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53