(color online) (a) Schematic of two-terminal graphene field effect transistor (GFET). (b) I–V curves of six graphene samples taken through electrical breakdown. All graphene channels have a width of 5 μ m and a length of 10 μ m . (c) I–V measurement from 0 to 0.5 V. (d) The breakdown current density J of the six samples.