Laser-induced graphene-like carbon for volatile organic compound sensing

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Murray, Richard
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University College Cork
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Laser-induced graphene-like carbon (LIG) is a potential resource-efficient fabrication route to support the abundance of sensors required by Industry 4.0 for IoT edge sensing applications, including wearables and worker safety LIG is formed \textit{in situ} by laser irradiation of suitable precursors, e.g. polyimide, to yield conductive, porous, 3D foams comprised of graphene sheetlets. This direct conversion allows for good spatial resolution (~ 50 um) and arbitrary pattern design, thus enabling the prototyping of diverse devices ranging from supercapacitors and interdigitated electrodes to electrochemical and Volatile Organic Compound (VOC) sensors. This thesis develops resource efficient, iterative system-agnostic optimisation procedures for LIG fabrication and novel back-contacting routes. Iterative use of design of experiments optimisation provides robust investigative route to determine ideal conditions with minimal investment of time and resources. An all-laser process of achieving back contacts from LIG to underlying metal was also demonstrated. Unlike current mechanical or silver paint contacts, back-contacts decouple the mechanical and electrical interface to external electronics, thus improving system reproducibility and, preventing surface contamination of the active material. Further, this scalable approach is a promising device integration route for both wafer-scale and printable electronics. Low-resource, low-power chemiresistive VOC sensors are also reported, comprised of low mass loadings of SnO nanoflowers (synthesised below 100oC and at ambient room pressure) on LIG electrodes. These offer a low-energy alternative to standard VOC sensors, which typically require high operational and fabrication temperatures (>300oC). These chemiresistive sensors can detect methanol vapor at laboratory temperature, with a limit of detection (170+/-40 ppm), below 8-hour exposure levels for worker safety (200 ppm). The sensors also demonstrated stable DC resistance responses \Delta R/R = 9+/-2% to 710 ppm of methanol for over 21 days in ambient conditions.
Volatile organic compound sensing , Additive manufacture , Nanomaterials , Graphene , Laser-induced graphene
Murray, R. 2023. Laser-induced graphene-like carbon for volatile organic compound sensing. PhD Thesis, University College Cork.