Two-dimensional materials, also known as two-dimensional atomic crystal materials, refer to materials in which electrons can move freely only in two dimensions at the non-nanoscale range of 1–100 nm, namely planar motion. These materials include graphene, boron nitride, molybdenum disulfide, tungsten disulfide, molybdenum diselenide and MXene. Graphene features single-atomic-layer thickness and high carrier mobility.