One-step fabrication of graphene sensors by femtosecond laser direct writing

The unique features of femtosecond laser, such as high peak power and ultrashort pulse width, extend its applicability to advanced processing of a broad range of materials including polymers, metals, semiconductors and novel two-dimensional materials. In this work, a direct writing platform employing a femtosecond Er-doped fiber laser as the beam source has been established for one-step fabrication of graphene-based sensors in a cost-effective and scalable manner. In-plane humidity sensors have been directly fabricated by patterning and reducing the graphene oxide (GO) thin films. The reduced GO (rGO) patterns are good electrical conductor due to the effective removal of oxygen-containing groups by infrared laser irradiation, thus functioning as the electrodes of the sensors, while the pristine GO thin films act as the sensing materials towards moisture stimuli. The as-fabricated humidity sensor shows high sensitivity and fast responses to humidity change. As a proof-of-concept demonstration, the device exhibits real-time sensing capability towards a human finger, which can be envisioned as a promising candidate for non-contact human-machine interface applications.