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Direct laser writing of pyrolytic carbon microelectrodes

Project type: Ph.D. project
Project responsible: Emil Ludvigsen
Supervisors: Stephan Sylvest Keller and Jenny Katarina Emnéus
Partners involved: DTU Nanolab, DTU Bioengineering
Project start: 2019-06-01
Thesis - link to the thesis in orbit: N/A

Project description

This project investigates how direct laser writing (DLW) may be employed for the fabrication of carbon microelectrodes by converting insulating carbon precursors such as polymers into conductive carbon traces through a process called local laser pyrolysis (LLP).

Carbon is an excellent electrode material for all sorts of applications, such as sensors [1, 2], super-capacitors [3], and biological scaffolds [4]. The reason for this is that carbon has a wide potential window [5], a high chemical stability [5], is biocompatible [4], cheap, and readily available [5]. Accurate patterning of the carbon electrodes rely on the patterning of the carbon precursor. This can be done by mold casting, UV-lithography [4, 6, 7], additive manufacturing [7], and DLW [1, 2]. The main advantage of DLW is the highly localized heating, which eliminates the need for a high-temperature compatible substrate during the pyrolysis of the carbon precursor. This reduces the overall thermal budget of the process and allows for writing carbon electrodes on flexible substrates [1, 2].

So far, the project has mainly focused on LLP of SU-8, which has been modified by the inclusion of an absorber into the resin, in order for the SU-8 to absorb the laser light. The laser light is absorbed by the absorber in the SU-8 and due to the poor thermal conductivity, and the narrow spot size (ca. 32 µm) of the laser, a very rapid and local heating occur. Above ca. 900℃, the SU-8 is pyrolysed [4, 8], i.e. all non-carbonic species are ablated and only a distinct trace of carbon remains. The carbon is porous and conductive, thus making it a potent candidate for the abovementioned applications. The project is funded by the European Research Council (ERC) under the Horizon 2020 framework programme grant no. 772370-PHOENEEX.

Publications

Selective Direct Laser Writing of Carbon Microelectrodes in Absorber-Modified SU-8

https://www.mdpi.com/2072-666X/12/5/564

Fabrication: Process Flows

References

[1]: Luo, S., Hoang, P. T., & Liu, T. (2016). Direct laser writing for creating porous graphitic structures and their use for flexible and highly sensitive sensor and sensor arrays. Carbon, 96, 522-531.
[2]: Rahimi, R., Ochoa, M., Tamayol, A., Khalili, S., Khademhosseini, A., & Ziaie, B. (2017). Highly stretchable potentiometric pH sensor fabricated via laser carbonization and machining of Carbon− Polyaniline composite. ACS applied materials & interfaces, 9(10), 9015-9023.
[3]: El-Kady, M. F., Ihns, M., Li, M., Hwang, J. Y., Mousavi, M. F., Chaney, L., Lech, A. T., & Kaner, R. B. (2015). Engineering three-dimensional hybrid supercapacitors and microsupercapacitors for high-performance integrated energy storage. Proceedings of the National Academy of Sciences, 112(14), 4233-4238.
[4]: Amato, L. (2013). Pyrolysed Carbon Scaffold for Bioelectrochemistry in Life Science. Kgs. Lyngby: Technical University of Denmark.
[5]: McCreery, R. L. (2008). Advanced carbon electrode materials for molecular electrochemistry. Chemical reviews, 108(7), 2646-2687.
[6]: Hemanth, S., Halder, A., Caviglia, C., Chi, Q., & Keller, S. S. (2018). 3D Carbon microelectrodes with bio-functionalized graphene for electrochemical biosensing. Biosensors, 8(3), 70.
[7]: http://labadviser.nanolab.dtu.dk/index.php/LabAdviser/Technology_Research/Cleanroom_fabrication_of_3D_electrodes_with_lithography_and_pyrolysis
[8]: Martinez-Duarte, R. (2014). SU-8 Photolithography as a Toolbox for Carbon MEMS. Micromachines, 5(3), 766-782.