C60 molecules have an intriguing ball-shaped structure that
suggests several interesting possibilities for motion on surfaces.
Indeed, researchers have found that the passage of electrons through a
bucky ball in a transistor is correlated to the spinning of the ball
around its center of mass. Moreover, since bucky balls look like
molecular ball bearings, it has been thought that they may be useful as
lubricants for use in automobile brakes.
Now a team of researchers at
the University of Bologna (Italy) and the University of Liverpool (UK)
have carried out detailed molecular dynamics simulations to understand
the motion of bucky balls on metal surfaces.
Francesco Zerbetto and Gilberto Teobaldi have found that C60
molecules exhibit a wide range of molecular motions on surfaces. The
bucky balls spin and bounce on the surface and also show an intercage
rattling motion that Zerbetto says is similar to that of billiard
balls in a partly filled roll-a-rack triangle. The simulations have
been carried out as a function of temperature and model the movement
of several bucky ball molecules over times ranging up to one
nanosecond. There is some transfer of charge from the gold surface to
the bucky ball that helps in the adsorption of these molecules at the
surface. The researchers have found that with increasing temperature
the cages move away from the gold surfaces resulting in a lower
frequency of bouncing. The bouncing frequencies obtained by simulation
match very nicely with experimental measurements of single-molecule
bucky-ball transistors, corroborating the validity of the simulations.
The researchers have found that the bouncing of the cage on the
surface and the intercage rattling govern the friction-related
properties of the bucky balls on a surface. �The strong van der Waals
interactions of the bucky balls with neighboring atoms makes the
friction far too high for lubrication�, said Zerbetto, but he is
hopeful that doping or chemical modification can be used to separate
the bucky balls to get them to act more like ball bearings.