Improved electrical conductivity of graphene film using thermal expansion-assisted hot pressing method

Achieving highly conductive graphene films requires the elimination of pores formed during the thermal reduction of graphene oxide (GO). Conventional methods such as hydraulic pressing often struggle to remove these pores effectively, especially in sub-micron large area films for uniform high pressure. In this study, we introduce a thermal expansion-assisted hot pressing (TEHP) technique that leverages the differential thermal expansion between graphite and tungsten to achieve pore-free, highly conductive graphene films. Here we heat the GO film sandwiched between graphite (high thermal expansion coefficient) and tungsten (low thermal expansion coefficient) to 1800 degrees C where pressures of 13-48 MPa are estimated. The TEHP resulted in graphene films with a smooth, metallic surface, free of macropores. Raman spectroscopy and electron microscopy analyses confirmed the enhanced crystallinity and compactness of the films. The electrical conductivity of the hot-pressed graphene films shows a threefold improvement over normally annealed films. This scalable method offers a viable pathway for producing high-performance graphene films for advanced applications.