Effects of laser processing parameters on properties of laser-induced graphene by irradiating CO₂ laser on polyimide

The emerging technique of carbonization of polyimide (PI) by direct laser writing receives great attention for its flexibility, versatility, and ease-of-patterning capability in creating a variety of functional laser-induced graphene (LIG) sensors and devices. LIG prepared by CO₂ laser irradiating of the PI film is characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), specific surface area analyzer, synchronous thermal analysis, and Raman spectroscopy with the focus on investigating the effects of laser parameters (e.g., power, scanning speed) on the microstructure, thickness, and sheet resistance of LIG. Both TEM and XRD indicate that LIG is composed of many graphene layers with a layer spacing of 0.34 nm. The specific surface area of LIG decreases with the increase of laser power. The ratio of the thickness of LIG over the depth of the carbonized PI film as the expansion ratio characterizes the expansibility of LIG. The influence of image resolution and off-focus value on the sheet resistance of LIG is explained by the superposition mechanism of laser scanning spots.