One-step process for direct laser writing carbonization of NH₄H₂PO₄ treated cellulose paper and its use for facile fabrication of multifunctional force sensors with corrugated structures

It is highly desired to be able to readily and robustly fabricate carbon patterns on cellulose paper (CellP) with complicated 3D structures, which would allow for cost-effectively developing a variety of resilient and stable paper-based sensors. Upon a pretreatment of CellP with NH₄H₂PO₄, herein, we present a one-step direct laser writing carbonization (DLWc) method capable of in situ creating electrically conductive carbon features on the NH₄H₂PO₄ treated CellP. With assistance of infrared spectroscopy, thermogravimetry and differential scanning calorimetry, the role of NH₄H₂PO₄ in the pyrolysis/carbonization of cellulose paper to enhance the resultant carbon yield was investigated. The loadings of NH₄H₂PO₄ in CellP and the laser processing conditions were studied for their effects on morphology/structure and electrical property of the carbon line features created by DLWc on the NH₄H₂PO₄ treated CellP. Upon taking advantage of the unique mechanical characteristics of corrugated paper sheets, we further utilized the one-step DLWc process to fabricate disposable, lightweight, and low-cost paper-based sensors and demonstrated their use for sensing force, displacement, wind flow and finger-tapping position recognition. The one-step DLWc of CellP will lead a way towards large-scale, environmental-benign and cost-effective production of multifunctional paper-based sensors.