Optical anisotropy of laser-induced graphene films

Abstract

Films of laser-induced graphene (LIG) were obtained by line-by-line scanning of a cw CO2 laser beam over the surface of a polyimide (PI) film. It was found that the formation of a LIG layer with a thickness of about 60 μm occurs due to the pyrolysis of a thin surface layer of a PI film with a thickness of about 15 μm. The morphology of the synthesized film structure is shown to be significantly affected by the ratio between the laser beam diameter and the distance between the lines along which the laser beam moves. In the synthesized film structures, oriented light-reflecting carbon flakes have been found, which lead to the anisotropy of diffusely scattered light in the plane perpendicular to the plane of light incidence on the film. The observed phenomenon is characteristic of LIG synthesized with a cw laser, which provides a more homogeneous structure of graphene along the scanning line of the laser beam, compared to the graphene obtained with a repetitively pulsed laser. Our findings may help in the analysis of line-by-line cw laser scanning synthesized LIG and in the formation of film structures based on LIG for cold field electron emission technology.