Direct laser writing of pyrolytic carbon microelectrodes

Carbon microelectrodes are used in a variety of applications within energy storage, bisoensing, and detection of environmental contaminants due to their excellent material properties and low cost. However, the current fabrication strategies to achieve carbon electrodes with controlled and well-defined micro structures either involve the use of chemical binders and a master stamp, or the use of lithography and furnace pyrolysis, which requires a lot of energy. The aim of the research presented in this thesis was to explore the possibilities of directly and locally pyrolysing SU-8 photoresist using a focused laser beam. This is a faster and less energy costly approach since the micro-pattern is drawn directly in the resist thereby omitting the use of a master stamp, and the heating only happens locally thereby reducing the overall thermal budget. The concept of laser pyrolysis was proven and showed promising results in terms of the achieved electrical conductivity and the high degree of spatial control. The conditions for laser pyrolysis of SU-8 were investigated through experiments and finite element modelling, and the fabricated carbon microelectrodes were characterized in terms of their electrical, physical, and electrochemical properties. The laser pyrolysis process was optimized to maximize the electrical conductivity while minimizing the electrode line width. The carbon microelectrodes were then characterized electrochemically using both outer-sphere and inner-sphere redox probes, with the aim of optimizing the electrode design to maximize the redox signal. Finally, attempts were made to use the laser-pyrolysed carbon microelectrodes as transducer element in a biosensor.