Strongly Anisotropic Thermal Conductivity of Free-Standing Reduced Graphene Oxide Films Annealed at High Temperature

Thermal conductivity of free-standing reduced graphene oxide films subjected to a high-temperature treatment of up to 1000 degrees C is investigated. It is found that the high-temperature annealing dramatically increases the in-plane thermal conductivity, K, of the films from approximate to 3 to approximate to 61 W m(-1) K-1 at room temperature. The cross-plane thermal conductivity, K-perpendicular to, reveals an interesting opposite trend of decreasing to a very small value of approximate to 0.09 W m(-1) K-1 in the reduced graphene oxide films annealed at 1000 degrees C. The obtained films demonstrate an exceptionally strong anisotropy of the thermal conductivity, K/K-perpendicular to approximate to 675, which is substantially larger even than in the high-quality graphite. The electrical resistivity of the annealed films reduces to 1-19 (-1). The observed modifications of the in-plane and cross-plane thermal conductivity components resulting in an unusual K/K-perpendicular to anisotropy are explained theoretically. The theoretical analysis suggests that K can reach as high as approximate to 500 W m(-1) K-1 with the increase in the sp(2) domain size and further reduction of the oxygen content. The strongly anisotropic heat conduction properties of these films can be useful for applications in thermal management.