Extensive reduction of graphene oxide on thin polymer substrates by ultrafast laser for robust flexible sensor applications

Low-cost, flexible wearable graphene-based sensors demand a high-quality and highly conductive graphene. The scalable production of graphene is challenged by complexity, cost, and energy requirements resulting in no direct facile method for volume production. Reduced graphene oxide (rGO) is a promising graphene derivative that could serve as an alternative with similar properties of graphene. Graphene oxide (GO) is an electrical insulator due to distorted sp2 bonding and is transformed to rGO by eliminating oxygen through a reduction process. We report an extensive reduction of oxygen in GO films with producing high quality rGO on flexible polyimide (PI) and polyethylene terephthalate (PET) substrates using ultrashort laser pulses. After laser reduction, the sheet resistance of GO significantly reduces from M omega Sq-1 to few hundreds omega Sq-1 where the C/O ratio enhances from 1.8 to 10.0 obtained from XPS analysis. Raman spectroscopy revealed highly conductive rGO thin film where the ID/IG ratio decreases from 0.94 to 0.27, and I2D/IG ratio increases from 0.12 to 0.63 confirming the restoration of sp2 carbon as a result of laser reduction. The fabrication of LrGO based multifunction sensor and pH sensor with high sensitivity is demonstrated which provide a great potential for use in healthcare and flexible sensor applications.