(color online) Two-dimensional materials. (a) The band structure of graphene. Right: zoom in one of the band spectrum near the Dirac points.^[52] (b) Output characteristics of graphene field effect transistor, which prove that graphene can carry ultrahigh density current (over 1 μA/nm²).^[28] (c) Schematic of the MoS₂ breaking strength measurement. The effective Young’s modulus is comparable to that of steel.^[37] (d) Schematic of two-dimensional materials MoS₂, which belongs to the transition metal dichalcogenide family. A single layer is around 0.65 nm.^[36] (e) The photoluminescence spectra of monolayer and bilayer MoS₂ sample, which represents the MoS₂ band structure transition from indirect (corresponding to bilayer) to direct (corresponding to monolayer).^[38] (f) Transfer characteristics of single layer MoS₂ field effect transistor,^[36] which shows excellent electrical performance: for , the I_on/I_off ratio is greater than 10⁸.