Surface Morphological Growth Characteristics of Laser-Induced Graphene with UV Pulsed Laser and Sensor Applications

Generally, laser-induced graphene (LIG) is produced by carbonizing a polymer film by a laser. Such large-area laser scanning of a film involves various processing parameters. LIGs with different characteristics can be created by altering each processing variable. Therefore, it is necessary to investigate the characteristics of the LIG surface structure generated according to the entire laser processing parameter range. However, few studies have focused on the surface morphological properties of LIGs. In this study, the characteristics of LIGs generated on a polyimide (PI) film with different laser processing parameters were studied based on the surface morphology, and the LIG was applied to a humidity and ions-selective sensor. When the PI film was attached to the diagonal ramp, the distance in the z-axis direction of the processing surface was changed, leading to a gradual change in the beam spot diameter at the focusing point. Through this method, continuous energy changes were induced, and LIGs with various surface colors and shapes that can be distinguished with the naked eyes were produced. The LIG produced by this process was classified into five types, and the specific surface area, water absorption rate, contact angle, surface resistance, X-ray photoelectron spectroscopy, and the Raman spectrum were analyzed. Various distributions were observed according to the type of surface shape. These measured values affect sensor applications. We fabricated and tested humidity sensors and ion-selective electrodes and found that structures suitable for gas circulation with opened porous surfaces are sensitive to humidity change reactions, and structures with numerous active sites distributed due to the high specific surface area are suitable for ion exchange performance when coated with polymers. Sensor applications according to the surface morphology allow the existing LIG sensors to be further optimized in performance and production processes. Therefore, we propose a morphology-based method for LIG fabrication and sensor application.