Figure 4 - Electrical devices of semiconducting and metallic SWNTs.

a, Periodic array of source and drain electrodes (single device highlighted in red, scale bar 40 m, gap 20 m). b, Representative AFM image of thin-film, percolating SWNT network (scale bar = 1 m). The density of SWNTs per unit area is >10 times the percolation limit (Supplementary Fig. S7). c, Field-effect transistor geometry (s = source; g = gate; d = drain). The SWNT networks were formed on a 100-nm, thermally grown SiO₂ layer, which served as the gate dielectric. d, Inverse of sheet resistance as a function of gate bias for semiconducting (red, triangles) and metallic (blue, squares) SWNTs sorted in co-surfactant density gradients (characterized in Fig. 3e). The metallic SWNTs did not significantly switch with gate bias (<2), in contrast with the semiconducting SWNTs, which switched by a factor of >2  10⁴. (Error bars described in Supplementary Information, Methods.) The inset shows a semiconducting device plotted on a linear scale (red curve, same units). A lower bound for mobility in the semiconducting SWNTs is estimated (from the grey fit) to be 20 cm² V^-1 s^-1 (see Supplementary Information, Methods), comparable to previously reported mobilities for thin films of as-synthesized mixtures of metallic and semiconducting SWNTs near their percolation threshold²⁹.