Friction on a single MoS(2 )nanotube

Friction was measured on a single molybdenum disulfide (MoS(2)) nanotube and on a single MoS(2 )nano-onion for the first time. We used atomic force microscopy (AFM) operating in ultra-high vacuum at room temperature. The average coefficient of friction between the AFM tip and MoS(2 )nanotubes was found considerably below the corresponding values obtained from an air-cleaved MoS(2 )single crystal or graphite. We revealed a nontrivial dependency of friction on interaction strength between the nanotube and the underlying substrate. Friction on detached or weakly supported nanotubes by the substrate was several times smaller (0.023 ± 0.005) than that on well-supported nanotubes (0.08 ± 0.02). We propose an explanation of a quarter of a century old phenomena of higher friction found for intracrystalline (0.06) than for intercrystalline slip (0.025) in MoS(2). Friction test on a single MoS(2 )nano-onion revealed a combined gliding-rolling process. PACS, 62.20, 61.46.Fg, 68.37 Ps