Figure 2

AFM images of MoS ₂ nanotubes laid flat on the HOPG and friction results. (a) The nanotube, 230 nm in diameter, with marked place of the friction test; (b) the corresponding friction results using loads from 15 to 90 nN, COF 0.091 ± 0.005; (c) the nanotube, 240 nm in diameter, where three scan areas were tested; and (d) the corresponding friction results using loads from 3 to 15 nN, average COF 0.080 ± 0.006.