An ultralubricated system is reported which confines a C60 monolayer between graphite plates. C60 molecules act as molecular bearings, assisted by the nanogears of six-membered carbon rings between C60 molecules and graphite, in which the mean dynamical frictional forces are zero up to a high load of 100 nanonewtons. A stick-slip rolling model with a step rotation of a C60 molecule is proposed. This ultralubricated system, very promising for the realization of nano- and micromachines, is expected to open a new field of molecular bearings.
The MoS2 flake moves on MoS2 in such a way that the stacking of the
sulphur basal plane of MoS2 is maintained. The frictional forces
between MoS2 surfaces are clearly proportional to the loading force
although they depend strongly on the movement of the MoS2
flake. The Amontons-Coulomb law is excellently satisfied at loading
forces in the range of 1–120 nanonewtons. The frictional coefficient
between MoS2 surfaces along the direction [ 101̄0] of the
MoS2(0001) surface is estimated to be approximately 0.003.
The chirality of a multiwalled carbon nanotube (MWNT) on graphite has been determined to be of a zigzag type using frictional force microscopy. The force per angstrom required to rotate the zigzag MWNTs in-plane on graphite has been estimated to be approximately 4pN. Natural rolling induced by a tip contact appears in commensurate contact with a graphite surface. The difference between natural rolling and rolling with stick-slip lateral behavior is discussed.
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