▎ 摘　　要

One of the fundamental physical properties of graphene nanoribbons is its ability to conduct heat. Unfortunately, the precise microscopic mechanisms of heat conduction have also not been fully elucidated at room temperature when heat transport occurs in the two-dimensional material ballistically. The transport mechanism of ballistic heat conduction in graphene nanoribbons was investigated experimentally and theoretically. The dimensions of the two-dimensional material are substantially equal to or shorter than the average length that the phonons can travel freely. The thermal conductivity was determined experimentally and predicted theoretically under different dimension conditions, and the ability of the graphene nanoribbons to conduct heat ballistically was characterized. The boundary scattering effect arising from the crystallographic edge structure was evaluated, and the ballistic and diffusive transport characteristics were investigated. The results indicated that the heat conduction can be ballistic or diffusive, depending on the dimensions. With the decrease of the dimensions, heat conduction may begin to transition from diffusive to ballistic. This will inevitably lead to a considerable decrease in thermal conductivity. Transport can be ballistic even at room temperature, and ballistic effects may be noticeable. Graphene nanoribbons with larger dimensions may disadvantageously be used for applications in thermal management.